
Book._ 



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(mtm° l ^ l l 



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AN INTRODUCTORY COURSE OF 

LESSONS AND EXERCISES 

IN CHEMISTRY 

(REWRITTEN 1919) 



BY 

E. P. SCHOCH, Ph. D. 

Professor of Physical Chemistry, 
The University of Texas. 



Published by 

THE CHEMICAL LABORATORY 

OF THE UNIVERSITY OF TEXAS 



AN INTRODUCTORY COURSE OF 

LESSONS AND EXERCISES 

IN CHEMISTRY 

(REWRITTEN 1919) 

4% ■ 



BY 

E/P. SCHOCH, Ph. D. 

Professor of Physical Chemistry, 
The University of Texas. 



Published by 

THE CHEMICAL LABORATORY 

OF THE UNIVERSITY OF TEXAS 



QJj-23 
111*? 



Copyright. 1919 



E. P. SCHOCH 



.©CU535982 



-V 



ca 



S 



PEEFATOEY NOTE. 



This book aims to teach beginners the principles and facts 
which the chemist employes in his work, and the manner in which 
he solves his problems. It is thought that this manner of teach- 
ing the subject is more effective than the ordinary method of 
presenting descriptive chemistry. 

The book includes the usual subject matter presented to be- 
ginners, but arranged so as to emphasize general principles and 
general facts. It presents the special properties of substances 
primarily as illustrations of the general facts and principles pre- 
sented. One of the main features is the arranging of the subject 
matter with the view of presenting metathetical reactions thor- 
oughly before presenting oxidation-reduction reactions. Another 
feature is the basing of the study of oxidation-reduction reactions 
on a thorough study of battery cells. The third main feature is 
a comparatively extensive and systematic presentation of organic 
chemistry. For a discussion of the pedagogic principles upon 
which this book has been developed, see Bulletin of the Univer- 
sity of Texas, "Chemistry in the High School/' Part III. 

In this rewriting of the book, the chief object was to make it 
self-contained: no other text is required in connection with the 
lessons and exercises in this book. 

However, it will be necessary for the student to secure other 
information in order to amplify and "round out" his knowledge 
of chemical facts. But the securing of such other information 
is an easier and more pleasant task than the drilling on funda- 
mentals provided for in this text. For years the author has been 
of the opinion that there should be two distinct types of text- 
books: one like this manual for drilling in fundamentals, and an- 
other for informational reading. This plan has been followed at 
the University of Texas with a fair degree of success for some 
years, and hence this text was rewritten and completed in accord- 
ance with this plan. 

Professor William A. Felsing of the University of Texas has 
contributed many notes, and has helped extensively in rewriting 
the book, appreciation of which is gratefully acknowledged by the 
author. 



TABLE OF CONTENTS. 



Chapter. Page. 

I. Fundamental Facts 1 

II. The Influence of Temperature Upon Chemical 
Changes, Illustrated Mainly with Experiments in 
Which Oxygen Plays the Chief Pole 18 

III. Simple Reactions Between Metals and Acids and the 

Preparation and Properties of Hydrogen 32 

IV. The Molecular-Kinetic Structures of Gases and of 

Condensed Forms (Liquids and Solids) 39 

V. A Eeversible Chemical Reaction — Third Illustration 

of Equilibrium . 51 

VI. Acids, Bases, and Salts. .' 62 

VII. Ionization and the General Relation Between Dis- 
solved Acids, Bases, and Salts Which Results in 
Metathetical Reaction 73 

VIII. The Properties of Carbon, Sulphur, Ammonia, the 
Halogens, and of Some of Their Important Com- 
pounds 90 

IX. The Relative Weights of Molecules 112 

X. The Actions and LTses of General Reagents for Solu- 
tions of Salts (with a Scheme for Qualitative 
Analysis Limited to the Consideration of Some 
Common Compounds of Twenty Familiar Metal 
Cation's) i 118 

XL Electrolysis — The Chemical Changes at the Poles of 

Electrolytic Cells • 159 

XII. Battery Cells and Oxidation-Reduction Reactions... 168 

XIII. The Fundamental Principles of Organic Chemistry 

and the Chief Types of Organic Compounds 195 

XIV. Applied Organic Chemistry: Animal and Vegetable 
Fats and Oils, Carbohydrates, Cloth Fibers, and 
Nitrogenous Food Constituents 220 

Appendix — 

Table of the Elements With Their Atomic Weights 245 

Table of Pressures of Water Vapor 246 

Table of Metric Weights and Measures and Their Equiv- 
alents 246 

Relations of Temperature Scales 247 

Index " 249 



AN INTRODUCTORY COURSE OF LESSONS AND 
EXPERIMENTS IN CHEMISTRY. 

(Rewritten, 1919.) 



CHAPTEB I. 
FUNDAMENTAL FACTS. 

1. Introduction. 

It is a matter of daily experience to see wood, coal, oil, candles, 
etc., disappear when they burn; iron changing to a red powdery 
substance when it rusts; gunpowder, when ignited, changing to 
gaseous substances. These and many other marked, permanent 
changes in the properties of substances are called chemical 
changes, and the study of such changes is the object of chemistry. 

But there are many marked, permanent changes in substances 
which are not said to be chemical changes: ice changes to water 
at temperatures above its melting point and remains in the liquid 
form unless the temperature of its surroundings is lowered be- 
low the freezing point of water; a bar of steel may be mag- 
netized and may then behave as a magnet for an indefinitely 
long period. The student naturally asks: what are some of the 
defining characteristics of chemical changes ? 

We can answer this question partly by presenting the chief de- 
fining characteristic of chemical changes; but, before doing this, 
we must present some facts which are fundamental to the whole 
subject. 

2. Substances Exist in Only Three Different Forms — Solid, Liquid, 

and Gaseous. 

Most of us are familiar with the fact that water exists not only 
in the liquid form, but also in the solid form as ice and in the 
gaseous form as aqueous vapor. However, we must realize that 
not only water, but all other substances can exist in these three 
forms only: they exist in no other form. The experiments given 
below will acquaint the student with the fact that this is true of 
two substances other than water. Furthermore, we must realize 
that any definite weight of a substance in any one of these forms 
will have the same weight when changed to either of the other 
two forms, — in other words, a change in form, as for instance 
from the solid to the liquid or to the gaseous form, will not entail 
a gain or loss of weight. This also is demonstrated in the experi- 
ments below. 



2 Schoch: Introductory Chemistry 

The Note Boole. — Since the student should begin at once to 
"write up" his experiments, a few directions concerning the man- 
ner of writing these notes will be in order here. 

The notes should be written up periodically shortly after, but 
not during, the performance of an experiment. 

The first thing needed in a note book is correct spelling, correct English, 
good penmanship and general neatness. Headings should be capitalized 
and underscored, the body of the "write-up" properly paragraphed, and 
the notes not crowded together. 

All attempts to use blanks, to be filled in. or detailed "patterns," to be 
followed for the writing up of experiments, are to be avoided. A few 
general directions are naturally to be followed, but any approach to a 
"formula" to be used in writing up experiments should be decidedly 
avoided. 

The experiments should not be numbered. The most important thing 
is to devise for each experiment a heading which states clearly the nature 
and object of the experiment. Considerable time should be spent in 
thought in order to devise headings that may be properly significant. A 
suitable heading is just as important as all the notes that follow. 

In the body of the "write-up." the first thing to be given is a direct 
reference to the directions followed: but the directions themselves should 
not be copied into the note book. Then should follow a brief, definite 
statement of what was actually noted or observed which has not been 
given in the printed directions referred to. 

The notes should always show the equations of the reactions in the 
experiment. 

The frequent drawing of figures, particularly of such things as test 
tubes, burners, etc., is a waste of time. A figure should be drawn only 
if the apparatus is so elaborate that the figure is essential to accuracy 
and brevity of description; and when a figure is drawn it should be 
drawn carefully — in projection or plan rather than in perspective. 

The following note on the experiment in Chapter II, Art. 2, may serve 
as an example of what is desired: 

EXAMPLE OF NOTE BOOK ENTRY. 

THE PREPARATION AND COLLECTION OF OXYGEN AND THE 
DEMONSTRATION OF SOME OF ITS PROPERTIES. 

The experiment in Chapter II, Art. 2, Schoch's Introductory Chemistry , 
was performed as given. 

It was observed that sulphur, carbon, phosphorus, and sodium, which 
had been heated to their kindling temperatures, burned vigorously in the 
oxygen gas. The product of the combustion of carbon is an invisible, in- 
odorous gas (carbon dioxide) ; that of sulphur is an invisible gas with a 
suffocating odor (sulphur dioxide) ; that of phosphorus is a white solid 
(phosphorus pentoxide) ; that of sodium also is a white solid (sodium 
oxide ) . 

Treated with water, the first three substances give solutions which 
turn blue litmus red, and the fourth gives a solution which turns red 
litmus blue. The formulae of the various chemical compounds and the 
quantitative relations in their formation are shown in the following 
equations : 

C-i-02=COo( carbon dioxide), etc. 

Incidental Experiment — Examination of Bunsen Burner. 
Examine a Bunsen burner. Take it entirely apart; then put it together 
again and light the gas. 



Chapter I 3 

Now turn the collar so that the air-holes are closed. The flame is 
yellow. Hold a piece of cardboard or a porcelain vessel in the flame; 
it becomes sooty. 

Open the holes. The flame now should not be yellow anywhere, and 
should be from six to seven inches in length. Insert a piece of cardboard 
or a porcelain vessel: soot is not deposited now. Hold a match or a 
splinter of wood across the flame near the base: t it will be burnt in two 
places, showing that there is an inner cooler region. Try inserting a 
match head into this cool region without lighting it. 

The inner tube of the burner occasionally becomes closed up. It is 
opened by scraping it out with a knife-blade, care being taken not to 
open it so much that the amount of gas admitted is larger than can be 
rendered non-luminous by the amount of air admitted by the air-holes. 

Cut off the supply of gas gradually by pinching the rubber tube. Sud- 
denly the flame will shoot down and will be seen burning below. Release 
the rubber tube, and note the odor and the color of the flame; note also 
that the burner gets hot. To get the burner to burn correctly, the gas 
must be turned off and lighted again. When a small flame is needed, 
the air supply must be cut off in proportion to the gas. 

Experiment. — (a) Secure a test-tube of the size ordinarily used; have 
it fairly clean but quite dry, and put into it as much powdered sulphur 
as will fill the tube about 1 cm., or one-half inch in length. 

Have an instructor assign you to a fairly sensitive chemical balance, 
and learn how to use it. Note the number of the balance, and use only 
the same balance in any one experiment. With the aid of a loop of 
copper wire, suspend the filled test-tube from the balance pan hook, and 
ascertain the total weight of wire loop, test-tube, and sulphur. Make a 
temporary record of this weight on a piece of paper. 

Light a Bunsen burner, and turn down the gas until the length of 
the flame does not exceed seven to eight centimeters (about three inches, 
since 1 inch equals 2.5 cm.). Grasp the test-tube near its open end with 
a holder, and put the lower, filled end into, or just above, the flame to 
heat the sulphur. Move the end of the test-tube to and fro slightly so that 
the flame may "lick" around the tube and heat all sides evenly. Allow 
the tube to be heated until the sulphur has melted and most of it dis- 
tilled out of the bottom of the tube. Do not heat the tube farther than 
about 3 cm. from the closed end so as to avoid expelling any sulphur 
from the tube. 

When through heating, hold the tube out of the flame to cool it for a 
few minutes, and then lay it aside on a dry towel until it is fairly cool. 
Then weigh the tube and contents on the same balance you used before, 
employing the same copper wire loop to suspend it. 

If none of the contents were spilled mechanically, the tube and con- 
tents will be found to have the same weight as before, which shows that 
sulphur undergoes no change in weight while it is melted or vaporized. 

Some one might object that we are weighting the 'sulphur in a solid 
state in both instances, and that it might have a different weight while 
hot and in the form of vapor. While this objection is a valid one, yet 
it should be pointed out that these various experiments performed by 
the student are merely for the purpose of indicating something of • the 
correctness of a statement so as to predispose the student to accept the 
rest of the statement on faith. It is difficult to weigh a hot body, because 
the air currents started by a hot body tend to lift it and thus falsify 
the weight. However, having obtained the result above, the student is 
inclined to believe the further statement that even the hot vapor of the 
sulphur has the same weight as the solid sulphur. 

(b) Repeat the above experiment with naphthalene. This substance 
is familiarly known as "moth balls." 



4 Schoch: Intboductory Chemistry 

Note that both of these substances change readily from one form to 
another, but that they exist in three different forms only; and that these 
changes in form do not entail changes in weight. 

3. Even the Most Complex Changes in Matter Do Not Increase or 
Decrease the Weight of the Material Involved (Law of the 
Indestructibility of Matter). 

Although it is easily seen and readily admitted by most of us 
that such simple changes as the melting of a substance or the 
evaporation of a liquid will not cause an increase or decrease in 
the amount (weight) of the material involved, yet we wish to 
have some further demonstration to convince us that matter will 
not gain or lose weight when subjected to changes which appear 
to be more extensive. For this purpose the experiments given be- 
low are here inserted. They show that, when substances undergo 
such marked changes as to produce new substances, even then the 
total weight of the material after the change is the same as it 
was before. 

Experiments. — (a) To be performed by the teacher only. Secure a 
U-tube about 20 to 25 cm. (8 to 10 inches) in height, and 15 to 20 mm. 
in diameter, and fit one of the open ends with a two-hole rubber stopper. 
Secure two pieces of ordinary small glass tubing 15 cm. in length, and 
bend them at the mid-points to angles of about 45°, and "fire-polish" 
the ends. Secure two ordinary test-tubes, fit each with a one-hole stop- 
per, and by moans of the bent pieces of glass tubing, connect these 
through the two-hole rubber stopper with one opening of the U-tube. 
Put about 2 c.c. of concentrated ammonia solution into one test-tube, 
and about 2 c.c. of concentrated hydrochloric acid into the other. By 
means of a wire loop, suspend the Avhole apparatus on one arm of a 
large, delicate balance, and ascertain its weight. Then, grasp the U-tube 
near its open end, immerse it in some ice water, and warm both liquids 
simultaneously by means of two small flames. The heating should be 
moderate, and well regulated so that both liquids may boil at the same 
rate, and so slowly that none of the products are projected out of the 
open end of the U-tube. 

Note the dense, white clouds and solid deposits of ammonium chloride 
formed. This substance is formed by direct chemical union of the hy- 
drochloric acid gas with the ammonia gas. 

Heat the liquids for about one minute at the longest. Then take the 
U-tube out of the water, dry it well, and weigh it again on the same bal- 
ance. If nothing was expelled mechanically from the U-tube, the ap- 
paratus and contents will weigh just as much as before, which shows 
that any definite amount of matter has the same weight irrespective of 
any extensive chemical change which it may have undergone. 

\b) Secure about 2 grams of lead in the form of thin sheets (or, less 
suitably, some tinfoil)." Tear it into strips about 5 cm. in length and 
roll it "with slight pressure into a ball, or wad, to drop it into an ordi- 
nary test-tube. Cover this ball with powdered sulphur, wipe the test- 
tube clean on the outside, and weigh it with its contents (suspending it 
on the balance pan hook by means of a loop of wire). Then grasp the 
test-tube at its upper end with a test-tube clamp, and heat the lower end 
of the test-tube fairly strongly until a progressive glow in the metal in- 
dicates that the sulphur is uniting with the metal! If this heating is 
done cautiously, nothing will be expelled mechanically from the^ test-tube, 
and the only changes in the contents will be due to the chemical union 



Chapteb I 5 

of some of the sulphur with the metal. Hold the test-tube in the air for 
a while to cool, then lay it on a dry cloth until it is quite cool. Finally, 
weigh it again on the same balance with the same loop of wire with 
which it was previously weighed. It will be found to have undergone 
no change in weight. 

Since weight is merely a measure of the quantities of substances 
or matter, the fact just stated shows that when substances undergo 
physical or chemical changes, the total amount of matter con- 
cerned does not change: — this general fact is known as the Law 
of the Indestructibility of Matter, and the value of knowing this 
fundamental law lies in the fact that by weighing, before and 
after a change, the various substances concerned in it, we find how 
much of each original substance has entered into the composition 
of the different resulting substances. In other words, the balance 
enables us to find out exactly what has happened during a change. 
Furthermore, the balance is the only generally applicable means 
with which this can be found out. While it is true that, in 
special instances, changes in the composition of substances can be 
noticed by means of one of our senses — sight, taste, feeling, etc., 
yet even then we do not perceive whether the change in composi- 
tion is due to an addition of matter or to an abstraction of mat- 
ter; but the balance reveals not only changes in the composition 
of matter, but it also tells us whether the change is due to an 
addition or an abstraction of one part of matter to or from an- 
other part. Therefore, the establishment of the Law of the In- 
destructibility of Matter made weighing the first unfailing and 
generally applicable means for ascertaining exactly what happens 
in chemical changes. Lavoisier was the first man who showed 
that matter is neither created nor destroyed by means of chemical 
changes (1774), hence he is called the founder of chemistry. 

4. The Fundamental or Defining' Characteristic of Chemical 
Changes: — Law of Definite Proportion. 

Let us compare two changes which in their outer aspects re- 
semble each other, but only one of which is a chemical change, 
and let us point out the fundamental characteristic which distin- 
guishes this chemical change from the other, — and hence from 
all other kinds of change. Let us take the decomposition of po- 
tassium chlorate at high temperatures — which is shown in the 
experiment below — and compare it with the drying of fruits or 
vegetables. In both cases, the solids lose weight — the potassium 
chlorate through the loss of oxygen, and the fruit through the loss 
of water — both of which escape as gases into the atmosphere. 
After the lapse of sufficient time, both changes cease, and the 
remnants will not lose any more weight. By dividing the total 
loss from each substance by the total amount of the substance 
taken, we obtain the loss per unit amount of each. Other por- 



6 Schoch: Introductory Chemistry • 

tions of potassium chlorate and of the same vegetable are then 
subjected to the same operation at the same or slightly different 
temperatures. The maximum loss experienced in these operations 
are again noted, and the losses per unit amounts are calculated. 

The fundamental difference between these two changes lies in 
the fact that the loss of weight shown by any particular amount 
of potassium chlorate, such as one gram, is always exactly the 
same — namely, it is as near to 0.392 grams as the delicacy of the 
balance and the care taken in the operation makes possible. But 
the loss of weight shown by one gram of a potato on drying will 
vary from 0.65 grams to 0.85 grams, depending on the source and 
kind of potato; and, although the average loss is 0.75 grams, yet 
the result obtained with any potato will, in many cases, be differ- 
ent from this average result, even when the balance used is ex- 
ceedingly delicate and the manipulation perfectly correct. We 
know the percentage of water in potatoes is never exactly the 
same, although it may be roughly the same. But the percentage 
of oxygen in potassium chlorate of all makes and from all sources is 
always the same — 39.2 per cent — and this exact quantitative re- 
lation between the original and the resulting substances in a chem- 
ical reaction is the defining characteristic by means of which we 
distinguish between those changes which we call chemical from 
those which we designate as physical, etc. 

The second experiment given below also illustrates this defin- 
ing characteristic of chemical changes. It will be found that a 
definite weight of copper — say, 1 gram — will combine with as 
nearly 0.252 grams of sulphur as the method of operation renders 
possible. 

Experiment. — Secure a small porcelain crucible (20 c.c.) and lid, a 
clay covered triangle, an iron ring-stand, and a Bunsen burner. Put the 
burner on the base of the ring-stand, clamp the 4-inch ring of the ring- 
stand in proper position for heating objects placed on the ring, put the 
clay covered triangle upon the ring, and the crucible on the triangle. As- 
certain from an instructor whether or not you have arranged the apparatus 
correctly. Light the burner and warm the crucible and lid gently for 
a minute. Then allow them to cool, take them to a "quantitative" (or 
sensitive) balance, and ascertain their weight (instruction!). Fingers 
touching the crucible should clean and dry! Record the weight of cruci- 
ble and lid on some convenient piece of paper. Then secure a small bot- 
tle of pure potassium chlorate, and with the aid of a small, clean por- 
celain spoon transfer about one gram of this substance to the crucible. 
Then weigh the crucible and lid again accurately. Record this weight 
and subtract the first weight from the latter to obtain the net weight of 
the potassium chlorate. Next place the crucible on the clay covered 
triangle again, and begin to warm it gently with a small non-luminous 
flame. Increase the flame so slowly that decrepitation is reduced to a 
minimum, but continue until the crucible is heated by the full strength 
of the burner flame. Turn out the flame, allow the crucible to cool, and 
weigh it again. Record this weight and subtract the first weight (abo**) 
to obtain the net weight of the residue. Divide the weight of the residue 
by the weight of the potassium chlorate taken, and record the result. 



Chapter I 7 

Wash the salt out of the crucible and lid, wipe them dry, warm them 
as at the beginning above, and weigh them again for the second part of 
this experiment. 

Secure some pure, clean copper • in the form of very thin sheets or 
turnings. If it is in the form of sheets, cut or tear it into strips of 
about i cm. width and roll these loosely into balls. Put about 2 grams 
of copper into the dried, weighed crucible, and ascertain the exact addi- 
tional weight due to the copper. Note this on a piece of paper. Then 
put into the crucible about 2 grams of powdered sulphur (weighing it 
approximately), put the crucible on a triangle on an iron stand to 
heat it. Begin heating the crucible with a small flame until the sul- 
phur has melted, then increase the heat gradually until all the ex- 
cess of sulphur has been driven off (i. e., when the sulphur vapors cease 
appearing) : — stop heating promptly at this moment to avoid instituting 
a further change due to the action of the air upon the copper sulphide. 
Allow the crucible and contents to cool; then weigh it again carefully 
and note the weight on your piece of "note" paper. Subtract the weight 
of the crucible plus copper from the last weight, and divide the re- 
mainder by the weight of the copper: — the quotient should be nearly 
0.252. Record the result as follows: 

Ratio in which copper and sulphur combine to form copper sulphide, 
1:0.252. 

(Putting your own result in place of 0.252 here.) 

This experiment may be carried out equally well with lead in place 
of copper, but the ratio in which lead and sulphur combine is naturally 
different from that in which copper and sulphur combine. 

5. How Compounds Are Distinguished from Elements. 

The experiments under Art. 4 show that the weight relation of 
potassium chlorate to its residue is such as to show that potassium 
chlorate consists of — is a compound of — the residue plus some- 
thing else, and that the copper sulphide is a compound of copper 
and sulphur. 

A similar but extensive search with the aid of the balance has 
revealed that certain substances are never compoundable from 
others, and these substances are known as elements. 

6. Number and Kinds of Elements. 

At present about eighty different elements are known. Among 
them are many familiar substances such as sulphur, carbon (e. g., 
lampblack and charcoal), nitrogen (which constitutes 79 per cent 
of the volume of the air), metals such as iron, lead, zinc, copper, 
and many others. The elements are roughly classed into metals 
and non-metals* 

7. Mixtures and Compounds. 

When substances are simply put together — i. e., mixed — they 
do not necessarily form compounds with each other. Frequently, 
they remain side by side, unchanged, and could remain so indefi- 
nitely. Naturally, mixtures have only those properties which 
their constituents show separately. Compounds, however, have 



8 Schoch: Intkoductoky Chemistry 

new properties distinct from those possessed by their components. 
Yet in many instances it is difficult to determine whether or not 
any particular aggregate is a mixture or a compound of the dif- 
ferent substances in it, and the distinction can only be made with 
a wide knowledge of chemical facts. 



8. Derivation of the Atomic Weight Table. 

A study of the weight relations between reacting elements re- 
veals that we may find a set of numbers (one for each element), 
any two of which give either directly the ratio in which their cor- 
responding elements combine by weight, or they give this ratio 
after they have been multiplied by only simple factors, such as 2, 
8, J/-, etc. (Law of the Existence of a Set of Single Relative Com- 
bining Weights). 

By direct trial chemists found out years ago that the different 
elements combine or react with each other in different ratios, but 
the same elements always combine or react in the same ratios by 
weight. Thus they found out that, by weight, 

hydrogen 



oxygen 



sulphur 



carbon 



acts with oxygen 


in 


the 


ratic 


1:8 


" " sulphur 


H 


" 


M 


1:16 


" " carbon 


" 


H 


It 


1:3 


" " chlorine 


" 


" 


tt 


1.35.5 


" " calcium 


(( 


tt 


It 


1:20 


" " copper 


<( 


tt 


It 


1:31.8 


" " sulphur 


n 


ft 


ft 


1:1 


" " carbon 


.-. 


ft 


tt 


1:.375 


" " chlorine 


<( 


ft 


tt 


1:1.109 


" " calcium 


it 


it 


It 


1:2.5 


" " copper 


" 


it 


(( 


1:3.97 


" " carbon 


U 


ft 


ft 


1:.187 


" " chlorine 


a 


" 


" 


1:1.11 


11 " calcium 


" 


ft 


C " 


1:1.25 


" '• copper 


'•' 


if 


tt 


1:1.99 


" " chlorine 


ti 


tt 


ft 


1:11.83 


" " calcium 


(( 


it 


tt 


1:1.666 


" " copper 


u 


" 


tt 


1:2.66 



In order to record the weight relations in which all the differ- 
ent elements react to form the many thousands of compounds 
which exist, an almost interminable list would have to be made, 
and hence chemists have naturally tried for many years to sim- 
plify the manner of making these records. Of the many different 
schemes tried, only the following gave a useful result. The essen- 
tial part of this scheme consists in selecting some one element 
(hydrogen) and calculating the weight of each of the other ele- 
ments which is used up in reacting with unit amount of hydrogen 
either by direct reaction, or by reacting with as much of a third 
element as would itself react with unit amount of hydrogen. For 
the elements above which react direct with hydrogen, the first 
group of ratios give the numbers for this purpose. In order to 



Chapter I 9 

change the other ratios to fit this purpose, we proceed as follows : 
For example, to express the ratios by weight in which oxygen 
reacts with elements other than hydrogen, we take the correspond- 
ing ratios obtained from experiments, and recalculate them so 
that the amount of oxygen in all these ratios is 8, — that is, the 
amount of oxygen which reacts with 1 part of hydrogen. Eecal- 
culated in accordance with this idea, the experimental data above 
gives us — 

8 parts of oxygen react with 8 parts of sulphur 

8 " " " " " 3 " " carbon 

8 " " " " " 8.875 parts of chlorine 

8 " " " " " 20 " " calcium 

8 " " " " " 31.8 " " copper 

In order to do for sulphur what we did for hydrogen just now, 
we must use 16 parts sulphur in every ratio, because 16 parts 
sulphur react with 1 part hydrogen; hence the data above give, 
on recalculation, the following ratios by weight of sulphur react- 
ing with other elements than oxygen : 

16 parts sulphur react with 3 parts carbon 

" " " " " 17.76 " chlorine 

" " " " " 20 " calcium 

" " " " " 31.8 " copper 

In the same way we obtain the following figures for carbon : 

3 parts carbon react with 35.5 parts chlorine 
" " " " " 5 " calcium 

" " " " " 7.99 " copper 

For convenient inspection, we will place these four sets of 
ratios into the following table, placing at the top of the first col- 
umn the element hydrogen with the number 1, and below the ele- 
ments which react with it, together with the relative amounts of 
their weights which are used up in reacting with 1 part hydro- 
gen; then placing at the head of the second column the element 
oxygen with the number 8, — that is, the number of parts which 
combine with 1 part of hydrogen, which is the basal amount for 
the whole table, and this number for oxygen is to be placed in 
the same horizontal line in which it is placed in the first column. 
Then the elements with which oxygen reacts are placed in the 
second column on the same horizontal line in which they appear 
in the first column. In the same way we have arranged the third 
column for the compounds of sulphur with various elements with 
which it reacts, and the fourth column for the compounds of car- 
bon with the various elements with which it reacts. Thus we ob- 
tained the following table: 



10 



Schoch: Ixteoductory Chemistry 



PROPORTIONS BY WEIGHT DV WHICH CEBTAIN ELEMENTS REACT, 
AXD THE DEBITED REACTING WEIGHTS. 



Column I 


Column II 


Column III 


Column IV 


Column V 


1 part hydrogen 
with (below) — 






Reacting weights 

1 for hydrogen 


8 parts oxygen 


8 parts oxygen 
with (below) — 






8 for oxygen 


16 parts sulphur 


8 parts sulphur 


16 parts sulphur 
with (below) — 




8 for sulphuT 


3 parts carbon 


3 parts carbon 


3 parts carbon 


3 parts carbon 
Mow] — 


3 lor carbon 


35.5 parts 
chlorine 


8.875 parts 
chlorine 


17.75 parts 
chlorine 


35 . 5 parts 
chlorine 


8.875 for 
chlorine 


20 parts 
calcium 


20 parts 
calcium 


20 parts 
calcium 


5 parts 
calcium 


5 for calcium 


31.8 parts 
copper 


31.8 parts 
copper 


31 .1 parts 
copper 


7 . 99 parts 
copper 


7.99 for copper 



Next let us glance along every horizontal line in this table, 
pick out the smallest number occurring in that line, and put it in 
column V on the same lino. Thus we will obtain 1 for hydrogen, 
8 for oxygen, 8 for sulphur. 3 for carbon. 8.875 for chlorine, 5 
for calcium, and 7.99 for copper. 

It is evident that the numbers for any one element in the first 
four columns, for instance, for sulphur, are simple multiples of 
these smallest numbers in column V. Furthermore, any ratio in 
which the elements react may be written by using the numbers in 
column V, either directly or after they have been multiplied by 
only a simple factor — 2, 3. etc. Thus the ratio by weight in 
which hydrogen and oxygen combine is that of the two numbers 
in column V — 1 :8 : and the same is true for sulphur and oxygen 
for which the ratio is 8:8: while the reacting ratio for oxygen 
and calcium, though not 8:5. is obtained by multiplying the 5 
by 4, which gives the ratio 8 :20. Similarly the combining ratio 
for chlorine and carbon, though not 8.f - obtained by mul- 

tiplying the number of chlorine in column V by -i, which gives 
the correct ratio 35.5 :3. 

What has here been illustrated with a few elements is true for 
all elements: and column V, if lengthened out to include all ele- 
ments, gives a set of numbers, one for each element, which give, 
either at once, the ratio in which their corresponding elements 
combine by weight, or they give this ratio after they have been 
multiplied by only simple factors, such as 1. 2, or 3 (Law of the 
Existence of a Set of Sinsrle Eelative Combining Weights.) 



Chapter I 11 

9. The Atomic Structure of Matter. 

The two laws of combining weights pointed out in the forego- 
ing are due to the fact that (1) each element is made up of small 
particles (atoms) of the same weight and alike in every other 
way, which do not subdivide during chemical changes and which 
have the power to attract, or to hold on to, other atoms; (2) that 
the atoms of different elements have different weights; and (3) 
when elements combine to form compounds, their atoms combine 
in groups of two or three or four, etc., which groups are called 
molecules, and a quantity of any definite substance is merely a 
collection of groups or molecules of a particular kind. It fol- 
lows from the last statement that a compound must always con- 
tain its elements in exactly the same ratio by weight, and this 
accounts for the law of definite proportion. 

To understand how the atomic structure accounts for the ex- 
istence of a Set of Single Relative Combining Weights, let us as- 
sume that the numbers in column V are the relative weights of the 
atoms of the different elements. Thus, if a compound — e. g., car- 
bon bisulphide — is made up of groups or molecules containing one 
atom of carbon combined with two atoms of sulphur, then the 
ratio by weight in which these elements combine would be ob- 
tained by multiplying by 2 the number for sulphur in column V, 
which is actually the case. 

10. Atomic Weights. 

The numbers in column V are not the same as those given in 
Tables of Atomic Weights, because, in drawing up this table 
above, we did not consider the total amounts of each element in 
each molecule of the different compounds. However, when the 
latter is done we obtain the real atomic weights, and this will 
now be shown. The total amount of matter in a molecure — that 
is, the molecule weight — can be determined (as shown in Chap- 
ter VI). Thus the molecular weight of the hydrogen-oxygen 
compound, water, is found to be 18 times as heavy as the weight 
of an hydrogen atom; and since, in this compound the ratio of 
hydrogen to oxygen is 1:8, the amount of hydrogen in this mole- 
cule must be one-ninth of 18, or 2; and the total amount of 
oxygen must be eight-ninths of 18, or 16. These results would 
seem to indicate there are either two atoms of hydrogen 
(2X1=2), and also two atoms of oxygen (2X8=16) in each 
molecule of water, or that either or both atoms are twice as 
large: to decide this question, we draw up a table similar to the 
preceding one, in so far as we place, in each horizontal line, the 



12 



Schoch: Inteoductory Chemistry 



amount of one particular element in different compounds, and we 
select the proper number for the atomic weight by considering 
that the least amount of any particular element found in the 
molecule of any one of its compounds is the amount correspond- 
ing to one atom. 



Amount of Hydrogen 


Hyd. 

Water Sulphide 


Methane 
4 


Hyd. 
Chloride 




Least amount of 




2 2 


mol. 1 


Amount of Oxygen in 


Sulphurous 


Carbonic 
acid 


Chlorine 


Calc. 

oxide 

16 


Least amount of 




16 32 


32 


32 


16 


Amount of Sulphur 


Sulphurous ', Hyd. 
acid Sulphide 
32 32 


Carbon 

bisulphide 

64 


Sulphur 

dichloride 

32 


Calc. 

Sulphide 

32 


Least amount of 
Sulphur in any mol. 
32 










Amount of Carbon in 
mol. of 


Carb. Carbonic 
Methane bisulphide acid 
12 12 12 


Carbon 

Tetra-CL 

12 


Calc. 

Carb. 

24 


Least amount of 
Carbon in any mol . 
12 


Amount of Chlorine 
in mol. of 


Hyd. Sulphue 
Chloride di chloride 
35.5 71 


Carbon 
Tetra- 
chloride 
142.0 


Chlorine 
oxide 
35.5 


Calc. 

Chloride 

71 


Least amount of 
Chlorine in any mol. 
35.5 







Strictly speaking, the values of the atomic weights now em- 
ployed are not exactly those given above — which were obtained 
with the weight of the hydrogen atom assumed equal to one, but 
they are values obtained with the weight of the hydrogen atom 
equal to 1.008 nearly, so chosen as to make the value of the 
weight of the oxygen atom exactly 16. 



11. A Set of Symbols for Expressing Weight Relations in Com- 
pounds. 

To represent the atoms and the atomic weights of elements, 
chemists use the initial letter of the name (English or Latin) 
of each element (sometimes coupled with an additional letter). 
The formula of a compound is expressed by writing, side by side, 
the symbols of all the elements in its molecules. Thus the for- 
mula for potassium chlorate is written thus — KC10 3 — which 
means that its molecule contains one atom or 39 parts by weight 
of potassium, plus one atom or 35.5 parts by weight of chlorine, 
plus three atoms or 3X16 parts by weight of oxygen. 

To express the weight relations for the change which potassium 
chlorate undergoes in the first experiment under Article 4, we 
write — 2KC10,— 2KC14-30,, which means that two molecules of 
potassium chlorate in changing produce two molecules of the sub- 
stance denoted by KC1 (potassium chloride) and three molecules 
of oxygen (each of the latter being composed of two atoms). 
These svmbols also state that the number of parts by weight ex- 
pressed 'by 2KC1CX. which is 2(39+35.5+48) or 245. yield as 
many parts by weight of potassium chloride as are expressed by 



Chapter I 13 

2KC1, which is 2(39+35.5) or 149, and as many parts by weight 
of oxygen as are expressed by 30 2 , which is 3(16X2) or 96. 

12. Calculation of the Amounts of Substances Used in Practical 
Work. 

With the above expression the amount of oxygen obtained from 
different amounts of potassium chlorate is readily calculated. 
Thus to find how much oxygen is obtained by heating 5 grams, 
proceed as follows: 

Write down the symbolic expression (equation) for the rela- 
tions of the weight obtained by experimenters, — 2KC10 3 = 
2K01-j-30 2 ; underscore the symbols of the iwo substances with 
which the problem deals, — i. e., underscore 2KC10 3 and 30 2 . 
Put the "given weight" and "x" above the respective underscored 
symbols; and then put underneath these symbols the numbers 
which they designate, — thus 

5 x 

2KC1Q 8 =2KC1+3Q 2 

245 96 

Next, put the four numbers (including x) into a proportion, 
reading each line in the same direction, say, from left to right, — 
thus 

5:x::245:96 



Solving for x gives the answer, 

5X96 



=1.96 



It is to be noted that the equation— 2KC10 3 =2KCl+30 2 — 
gives more information than is needed in this calculation; the 
extra amount is naturally to be neglected. 

Problems: Calculate how much potassium chlorate will give 5 
grams of potassium chloride. 

How much potassium chloride will be obtained when 10 grams 
of oxygen are obtained ? 

13. Table of the Elements Arranged in Accordance •with Their 
Natural Relations. 

If the names of the elements are arranged in the order of their 
"atomic numbers" (such numbers being obtained by certain fre- 
quency measurements of the X-ray radiations of the elements, see 
footnote I), which is generally also the order of their atomic 
weights, and if they are placed consecutively at equal intervals 
on a piece of tape and the tape wound on a suitable frame-work, 
as in the accompanying sketch, the vertical columns present the 
names of similar elements or of elements which are closely re- 
lated in properties. 



14 



Schoch: Introductory Chemistry 



^0 



20 



40 



60 



80 



100 



120 



140 



160 



180 



200 



220 



240 

oh 

II 



< ^R0U 




Harkin's Model of the Periodic System. 



Chapter I 15 

A simpler manner of printing the same arrangement is given 
in the table below. The first complete table of this kind was 
drawn up by the Eussian chemist. Mendelejeff, and simultaneously 
but independently by the German chemist, Lothar Meyer, in 1869. 
It is known as the Periodic System of the Elements, because from 
one element to the next similar element all the intervening ele- 
ments present a progression of properties which include all the 
different types, and which progression ends on the element sim- 
ilar to the initial element. Each set of elements showing such 
graduation of properties is known as a period, and the aggregate 
arrangement of the entire series of "periods" is known as the 
Periodic System. Stated briefly, the properties of the elements 
as well as the properties (see footnote 2) of their compounds 
form a periodic function or relation of the atomic numbers (or 
generally, atomic weights) of the elements. 

Exercise: Commit to memory the elements in the first two 
short periods and in the first long period. Memorize them in 
their exact order; memorize their symbols and their approximate 
atomic weights. 

Footnote 1: A very important and valuable method of deter- 
mining the atomic numbers of elements was dicovered by H. G. 
T. Moseley. He made a thorough and systematic study of the 
characteristic X-ray radiations (the "K" radiation) of the ele- 
ments, in which he found that the frequencies (f) of the radia- 
tions increase with increasing atomic weight of the element ac- 
cording to the simple relation 

f=k(A n — I) 2 

where k is a constant and A n is the atomic number. 

Footnote 2: Some of the properties referred to are malleabil- 
ity, ductility, melting points, specific gravity, coefficient of ex- 
pansion, latent heat of fusion (physical properties) and similarity 
of compounds, and the gradual transition of basic properties of 
the compounds of the elements on the left to acidic properties of 
the compounds of the elements on the right in a period (chemical 
properties). 

Questions on Chapter I. 

1. With what general experimental means or operation are 
compounds distinguished from elements? 

2. About how many elements are known? Mention a few 
elements that are commonly known. Into what two classes are 
elements divided? In general, what do the oxides of these two 
classes form on hydration? 

3. Why is the union of sulphur with copper considered to be 



16 



Schoch: I^tbodttctoby Chemistey 



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Chapter I 17 

a chemical change, but the dissolving of sugar in water not a 
chemical change? 

4. What is the most important use that chemical symbols 
serve ? 

5. State all the fundamental laws of matter set forth in this 
chapter. Who is the founder of systematic chemistry? State 
specifically what he did that earned him his title. 



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Chapter II 19 




Correct metnoa of holding 
and heating a test -tube 

than the oxygen in the atmosphere, and hence the splinter burns vigor- 
ously within the tube while, in the air, it glows merely. 

In the same manner, try lead peroxide (or dioxide), potassium nitrate, 
mercuric oxide, manganese dioxide (the latter requires a higher tempera- 
ture than the others and hence a hard glass test-tube must be used ) . 

3. Catalytic Action. 

Experiment. — Heat a small amount of potassium chlorate in a test- 
tube until it is barely melted, then sprinkle a little powdered manganese 
dioxide upon it. 

While performing the experiment above, note how much more 
rapidly the gas (oxygen) is evolved after the addition of the 
manganese dioxiae than before. The change still consists of the 
decomposition of potassium chlorate while the manganese dioxide 
remains unchanged in the reaction. Since the tendency to 
change which is exerted by the potassium chlorate is likely to be 
the same here as before because the conditions are the same, 
and since the reaction takes place much more rapidly, it follows 
that the manganese dioxide must affect the ease or difficulty with 
which the change takes place. This effect may be aptly com- 
pared to the effect of adding oil to the bearings of a piece of 
machinery. The oil does not increase the driving force of the 
machinery, but it lessens the resistance and thus helps to increase 
the speed with which the same force drives the machinery. Sub- 
stances which act like the manganese dioxide in this example are 
called "catalyzers." 

4. The Preparation of Several Bottles Full of Oxygen Gas and the 
Combustion of Several Elements in it. 

Experiment. — Secure a hard glass test-tube; fit it with a cork and a 
delivery tube as shown in the accompanying figure. For softening the 
cork, perforating it, and for bending the class tube, special directions 
will be given by the instructor. See also the figures below, which show 
how glass tubes are to be heated. Fill the test-tube half full with a 



20 



Schoch: Introductory Chemistry 



mixture composed of approximately two parts of potassium chlorate and 
one part manganese dioxide (powdered ). Be careful to keep paper, 
pieces of cork, and other combustibles out of this mixture. 

In the next operation, two students should work together. They should 
secure a water basin, four wide-mouth bottles, and four pieces of glass 
large enough to cover the mouths of tbe bottles. Assemble the whole as 



^ 



C G A 



burner for Bending 
Glass Tubing 



A Correctly Bent. 

B St C Incorrectly Bent- 



shown in the accompanying figure; heat the potassium chlorate and col- 
lect the gas. Secure a deflagrating spoon, put a small piece of charcoal 
in it, heat this in a burner Maine, and lower it into one of the bottles. 
In this same way, proceed to burn sulphur in another bottle, phosphorus 
in a third, and a small piece of sodium in the fourth. Add a little dis- 
tilled water to each of the bottles; shake the bottles with it so that the 
products of combustion may be absorbed by the water, and drop into 




each of the first three bottles a piece of blue litmus paper, and into the 
fourth bottle a piece of red litmus paper. The instructor will show the 
burning of iron (picture cord) in oxygen. Record in your note book all 
observations made in connection with this experiment. What properties 
of oxygen gas — solubility, etc. — has this experiment revealed? 



5. The Chemical Combining of Oxygen with Other Elements. 

The above experiment introduced the student to a chemical 
change which is the reverse — in a sense — of the separation of 



Chapter II 21 

oxygen from substances, — namely, the combining of oxygen with 
substances. The substances burned combine with oxygen in defi- 
nite relative amounts by weight. Thus 3 parts of carbon (char- 
coal) combine with 8 parts by weight of oxygen, and. this is ex- 
pressed by writing C0 2 — which means 12 parts by weight of 
carbon to 32 parts by weight of oxygen, and hence the same as 
3 :8. The product of the combustion of phosphorus contains the 
elements in the ratio by weight of 31 :40, — to express this we 
write P 2 a . The relation of the weights for the compound formed 
by sulphur is expressed by the formula S0 2 , that for sodium by 
the formula Na 2 and that for iron by the formula Fe 3 4 . 

Most elements combine with oxygen at high temperatures. With 
some elements this oxidation is accompanied with the evolution 
of little or no heat, and with others heat is absorbed. Some ele- 
ments (e. g., mercury and platinum) do not combine with oxygen 
except at low temperatures — and then usually very slowly. Aside 
from the absolutely non-active elements which form no compounds 
whatever (helium, argon, crypt on, neon, etc.), all the elements 
except fluorine form compounds with oxygen. 

6. The Hydration of Oxides. 

When, in the experiment under Article 4, the products of com- 
bustion are treated with water, the following reactions take place : 



CO, 
Carbon dioxide 


4- 


H 2 

Water 


= H 2 C0 8 

Carbonic acid 


S0 2 
Sulphur dioxide 


4- 


H 9 

Water 


= H 2 S0 3 

Sulphurous acid 


)sphorus pentoxide 


+ 


3ELO 

Water 


= 2H 3 P0 4 

Phosphoric acid 


]S T a 2 
Sodium oxide 


-f- 


H 2 

Water 


=i 2]\ T aOH 

Sodium hydroxide 



Iron oxide does not react with water. 

When substances react with water, as in the foregoing examples, 
they are said to become hydrated, and the reactions are known as 
hydrations. 

The hydration of oxides of "non-metals" (e. g., carbon, sulphur, 
phosphorus) generally produces compounds known as acids, solu- 
tions of which have a sour taste, and turn blue litmus red. The 
hydration of oxides of metals (e. g., sodium) generally produces 
basic hydroxides, solutions of which turn red litmus bine. 

The above facts, formula?, and equations should be accurately 
impressed upon the memory. 

Calculate how much water is required to hydrate five grams of 
each one of the oxides hydrated above. 



S : HOGH : IXTEODUCTOET ChEMISTKT 

T. Other Properties of Oxygen. 

Besides the properties of oxygen learned through the experi- 
ments above, the following quantitative data concernin, :: _ : 
is dee and her re g wen for convenient 

reference. At : C. and under 1 atmosphere pressure pure 
3 in water with which it is in contact to the 
approximately 4 volumes of the gas in 100 volumes of 
The solubility - see is given by volume instead of by 
a ht becat;- solubility of gas by volume is always - 

same irrespective of the extent to which it may be compr 

•Hows, of course, that the solubility by weight 
rferent with different press 
A 'iter oi oxygen - and under 1 atmosphere press 

_ grams is si _htly heavier than air because four- 

a of the ail s gas — g en — which is seven-eighths as heavy 

_n. 

becomes a liquid at — 118° C. and a pressure of 50 at- 
mosphere- lower tempera* res t liquefies, r remains 
liquid, under lesser pr 

8. The Proportion by Volume of the Oxygen in the Air (After 
Cooler). 

Id order to determine the volume o: a gas, air for 

example., a solution of potassium pyrogallate is employed to ab- 




sori the :: :~"_ n I leoease in volume is the volume of the 
z in the 

Experiment. — Secure a large test-tube or any slender, cylindrical ves- 
sel of 60-81 :. capacity, and fit it with a two-hole rubber stopper. Into 



Chapter II 23 

one liole push a short glass nozzle, and into the other a well-fitting plug 
of glass rodding. Secure a glass funnel, rubber tube, and pinch clamp 
and fit up the apparatus as shown in the accompanying figure. Test the 
apparatus to ascertain that it is air-tight. 

Secure 3 c.c. of a solution of pyrogallic acid, and 22 c.c. of a solution 
of potassium hydroxide, both of which have been prepared specially for 
this purpose, as follows: the first by dissolving 10 grams of pyrogallic 
acid in 30 c.c. of water, and the second by dissolving 240 grams of potas- 
sium hydroxide in 160 c.c. of water. (This will furnish enough for about 
ten experiments.) 

When ready to perform the experiment, mix the two solutions, pour 
the mixture into the funnel, and while the test-tube is removed, fill the 
rubber tube and nozzle with the liquid; then, while the second hole of 
the rubber stopper is open, fit the stopper into the test-tube; finally, 
close the second hole of the stopper with the plug. 

Without touching the test-tube except at the rubber stopper, open the 
pinch clamp: as soon as a few drops have entered the test-tube, they 
will absorb oxygen, and then the rest of the solution will flow in more 
rapidly. Close the clamp and invert the test-tube several times in order 
to bring the liquid thoroughly in contact with the enclosed air. Finally 
invert the test-tube, open the clamp and bring the level of the liquid, 
in the test-tube on a level with the liquid in the funnel; then close the 
clamp again, put the test-tube upright, and mark with paper labels or 
rubber rings the position of ( 1 ) the surface of the liquid in the test- 
tube and (2) the bottom of the stopper. 

Remove the test-tube and rinse it out with tap water. Then secure 
a burette, fill it with water, and with this ascertain the original volume 
of air in the test-tube and the volume of liquid which was drawn into 
the test-tube to fill the volume of the absorbed oxygen. Calculate what 
per cent, by volume, of the air is oxygen. 

9. The Determination of the Solubility of Air in Water. 

Half fill a 1 -liter bottle with distilled water, cork, and shake vigor- 
ously until the water is saturated with air. Take the temperature of 
the water and also the barometric reading. Fit a small flask (100 c.c.) 
with a one-hole cork and delivery tube. The tube should not extend be- 
yond the inner surface of the cork. Completely fill the whole apparatus, 
including the delivery tube, with the prepared water. Heat this to boil- 
ing and collect the gas in a small test-tube inverted into water. When 
no more gas comes over, equalize the levels of the water in the tube and 
trough and mark the level in the tube with a thin rubber ring (cut this 
from a piece of rubber tubing ) . To measure the volume which the air 
occupied, proceed as follows: Secure a burette, fill it with water to the 
zero mark (also fill the effluent tube to the tip). Then draw enough 
water from the burette to fill the test-tube up to the rubber ring, and 
read the amount drawn from the burette. Calculate the volume of air 
dissolved by 100 c.c. of water at the observed temperature and pressure ( ?) 

10. The Evolution or Absorption of Heat by Substances While 
Undergoing Chemical Changes. 

Just as in well-known physical changes some substances evolve 
heat — e. g., ice in freezing — and others absorb heat — e. g. ? liquids 
in evaporating — so in chemical changes some substances give up 
heat and others absorb heat. The evolution of heat during the 
combustion of sulphur, carbon, etc., in oxygen is plainly notice- 



v?4 - hoch: Introductory Chemistry 

able, but in many other instances one cannot become aware by 
any direct means that heat is absorbed or evolved. Thus when 
- -ium chlorate gives up oxygen, heat is given out just as in 
the combustion of sulphur in oxygen, but the amount Of heat 
produced is not very large and hen - not noticed beside the 

heat furnished by the burner. When potassium nitrate gives up 
oxygen, heat is actually lost, so that the burner flame must not 
only furnish heat to maintain the material at the high tempera- 
>ut it must also supply the heat which disapj 
The general observation to be drawn from these examp! 
that there - general rule concerning the evolution or absorp- 
tion of heat during chemical chan_ substances in chang- 
ing chemically absorb heat while others evolve heat. The fact 
That some sul ai - have to be heated while they react is no in- 
dication that they use up heat in changing: the heating may be 

ssary merely to produce and maintain the temperature n< 
sary for the rapid re - That is th» 

with potassium chlorate, which does not use up heat while it lib- 
-■• "■ gh.to 

keep b gh to continue to react. With combustible 

substances, the heat given up ~han enough to keep them 

at the temperature at which they react, and hence they continue 
to react (burn) without the aid of heat from another source. 

the quantity of heat resulting from a chemical 
re add to the chemical equation the amount of heat re- 
sulting from the reaction when as many grama of the substance 
are c as the numbers expressed by their symbols. Thus 

the equation — 

<-<\= 000 cal. 

is intended to express that when as many :' carbon as C 

stan"- that is. twelve) combine with as much oxygen gas 

is rtibines with this quantity of carbon (which ! ;rams 

of oxygen . then lories oi heat are evolved or obtained. 

Similarly, when we write — 

ZHgO=2Hg+O t — 43000 caL 

we mean tha~ in tfa decomposition of as many grams as 2HgO 
denotes in number (that is. 432) the amount of heat. 43000 
calories, disappears — is rendered 'atent within the resulting sub- 
stances A tork is the quantity of heat required by 1 gram of 
water to have its ire raised 1 : 

ft should be noted that these examples of thermochemical equa- 
tions show that, as the result of chemical changes, heat may either 
appear or disappear. It should be added that the amounts of heat 
which appear or disappear are verv ^mall in some instances. 

The thermochemical data for the other reactions mentioned in 
this lesson are here siven merelv for further illustration. 



Chapter II 25 

1. 2KC10 8 =2KCl+30oH-19500 cal. 

2. 2PbO„=2PbO+Oo+75400 cal. 

3. 2KN6 8 =2KN0 2 +Oo— 61120 cal. 

4. 2Ho+0,=2H,0 (at 18° C.) +136720 cal. 

5. S+O„=8O*+71080 cal. 

6. 4P+50o=2"PoO,+739800 cal. 

7. 7Na+O 2 =2Na,O+200520 cal. 

11. The Dependence of Chemical Changes Upon Surrounding Con- 

ditions. 

By this time the student is probably asking the question : what 
part does the heat play in these chemical changes? Is it to be 
looked upon as a force that impels the reaction? Since there are 
so many misconceptions possible concerning the influence of heat 
on chemical changes, an attempt will be made here to present the 
fundamental facts to the student before he acquires false ideas. 

Substances which react chemically are not made to react by 
forces acting upon them from without. They react on account 
of the existence of a natural tendency within them to react. This 
tendency may be increased or decreased by some condition con- 
trolled by the experimenter, but these conditions do not force the 
change to take place ; they merely increase or decrease the natural 
tendency to reaction which resides in the substances. 

The tendencies with which chemically reacting substances are 
impelled to change can be increased or decreased experimentally 
by only two different means : by changing the temperature, or by 
changing the concentration of one of the substances concerned in 
the change. The "concentration influence" will be discussed in 
later chapters, but the temperature influence will be considered 
right here. 

12. The Distinction Between Heat and Temperature. 

Heat and temperature must be carefully distinguished from 
each other : — they are not synonymous terms for one and the same 
thing, and, in general, their quantities are not proportional to 
each other. 

Temperature may be said to be the pressure or tendency with 
which the heat in a body tends to leave it, — just as the pressure 
in an automobile tire is the tendency with which the air com- 
pressed in it tends to escape. We may follow this comparison 
further to advantage : As more air is pumped into a tire, its 
pressure increases: just so the addition of heat to a substance 
from which it cannot escape increases the temperature of this 
space. In other words, the temperature rises as heat accumulates 
in a gi\en substance. Thus, when an incandescent electric light 
bulb is wrapped up in paper, clothing, or anything which prevents 



26 Schoch: Introductory Chemistry 

the radiation of the heat produced from the electric energy in the 
bulb, then the temperature of the bulb will rise steadily until 
some of the material is set on fire and it is destroyed. 

13. The Influence of Temperature Upon Chemical Changes. 

When a substance or a mixture of substances is not changing 
chemically the forces between the atoms and molecules in it are 
either prevented from acting by something akin to friction or to 
an obstruction, or they are perfectly balanced so that there is no 
excess of force tending to produce a change. 

In the first case, raising the temperature frequently lessens or 
removes the friction or obstruction ; hence raising the tempera- 
ture is the most general means employed for removing such re- 
sistances and "facilitating" chemical changes. In many cases, 
the resistance at ordinary temperatures is so great that the sub- 
stances do not react at all, while at higher temperatures the re- 
sistance disappears and the chemical forces in the substances are 
then able to propel the change more or less rapidly. The re- 
moval of resistance by a rise in temperature is quite regular: — 
the amount of substances changed is approximately doubled by 
every rise of 10° C. It is on this account that substances under- 
going chemical changes are usually heated. Xote the application 
of this in the experiments already performed. 

In the second case mentioned above, a chemical change will 
take place only when the conditions of equilibrium are changed. 
This also can be done through a change of temperature. How- 
ever, a temperature change may displace an equilibrium "toward 
either side," which means that a change in temperature may in- 
crease the reacting tendency of the original substances more or 
less than that of the resulting substances. The latter tend to 
change in the opposite sense from the original substances, or so as 
to produce the original substances again — they oppose the reac- 
tion of the original substances. Hence, as long as the two oppos- 
ing tendencies are equal, no change can take place ; but if through 
a change of temperature they become unequal, a change will en- 
sue in accordance with the relation of the two opposed reaction 
tendencies. This matter will be considered further in connection 
with the study of special examples of equilibrium presented 
later on. 

14. Connection Between an Evolution of Heat from a Reacting 

Mass and the Strength of the Reacting Forces. 

The general result concerning the heat, effect accompanying a 
reaction was stated above in Article 10 : the heat effect may be 
either "negative" or "positive." Hence, in general, there is no 
direct relation between the heat effect and the forces producing 



Chapter II 2? 

chemical changes. But when the amount of heat evolved is very 
large, then there is a rough connection between the heat effect and 
the forces producing such a change. This is due to the fact that 
negative heat effects and the forces which produce them are al- 
ways relatively small; hence, a reacting substance or mixture 
which evolves a great quantity of heat must have most of its forces 
acting so as to produce this heat — even if some of its forces would 
produce a (small) negative heat effect — and hence the total act- 
ing force and the quantity of heat are roughly proportional to 
each other (Thomsons Rule). This is illustrated in the reaction 
of oxygen with sulphur, phosphorus, carbon, and sodium, respec- 
tively, in all of which the vigor of the actions indicates that .the 
reacting tendencies are great, and we note the amounts of heat 
'evolved also are great; in other words, they are roughly propor- 
tional to each other. 

The production of great quantities of heat by some chemically 
reacting substances is due to conditions similar to those which 
result in the production of heat when a heavy body strikes the 
ground after falling through the air from a great height. If the 
body had been attached to a rope, the latter passed over a pulley, 
and a counterpoise attached on the other end of the rope, then 
the body would have raised the counterpoise while descending, 
and thus it would have spent its "energy of position" by per- 
forming the work of lifting the counterpoise. It also would have 
approached the bottom slowly, and hence not produced any heat 
on striking the ground. The energy thus spent in raising the 
counterpoise is the energy which appears as heat when the body 
falls freely to the ground. 

Substances or mixtures of substances which are capable of re- 
acting with the evolution of much heat possess potential energy 
just as the above body possesses potential energy before its fall. 
Whenever such substances undergo reaction with the production 
of heat, they lose this potential energy, and in its place we obtain 
the heat evolved. But when they are "hitched" up by a suitable 
chemical mechanism so that they will do work, then none, or 
very little, heat will appear — just as is the case when the descend- 
ing stone raises a weight. The galvanic battery is a good illus- 
tration of a "hitched up" chemical change : the reaction in the 
cell can take place only when an electric current is drawn from 
it, and through this current the reaction is doing work, — e. g., 
turning a motor, etc. 

We note that only a very small amount of heat is evolved in a 
battery cell when in action, but if the materials of the separate 
poles in a battery cell are brought into direct contact, then they 
will react without producing an electric current, or doing work, 
and in this case their reaction will be marked by the evolution of 
a large quantity of heat. 



28 Schoch: Ixteoductotcy Chemistry 

15. Chemical Equilibrium and Its Significance. 

In Article 11 of this chapter it is mentioned that when sub- 
stances react chemically they are impelled by internal forces and 
not by external forces; and in Article 13 it is stated that a sub- 
stance or a mixture of substance? which is not undergoing a change 
either has its internal forces balanced, or hindered from action 
by something akin to friction or to an obstruction. Since resist- 
ance or friction can be overcome by suitable means, it follows that 
every substance or mixture of substances with unbalanced internal 
forces will react until there is no remaining tendency for reac- 
tion. However, when the condition of rest has been attained, in- 
ternal acting forces are not absent: the} are merely balanced: or. 
in other words, only those substances or mixture of substances 
need be considered as oon-reactive which have their internal forces 
in equilibrium. 

At present we do not know enough about the forces in matter 
to be able to forecast whether or not a certain substance or mix- 
ture of substances will react. Hence, in the effort to learn to fore- 
cast whether or not a substance or a mixture of substances will 
react, chemists content themselves at present with learning, by 
trial, the conditions under which they are in equilibrium: it fol- 
lows that, under all other conditions, the substances are not in 
equilibrium, and hence wil to attain equilibrium con- 

ditions. Thus, it is seen that the ascertaining of equilibrium 
conditions is of prime importance in modern chemistry. 

This matter of determining equilibrium conditions is simpli- 
fied immensely by our knowledge that there are only a few factors 
which affect or determine equilibrium. These factors are: — 

(a) The concentration of each substance. 

(b) The temperature of the mixture. 

(c) The pressure upon the substance. 

Furthermore, the concentrations of the substances at equilibrium 
are limited in their conjoint variation by the "Law of Mass Ac- 
tion," and also the number of physical forms of each substance 
which may be present at equilibrium is limited bv the "Phase 
Law/' 

On account of these fundamental facts known concerning the 
relations of substances at equilibrium, and the further fact that 
substances when out of equilibrium react so as to attain- equili- 
brium, it is evident that equilibrium conditions are the means for 
deciding whether or not substances or a mixture of substances 
will react. 

The chief characteristic of a substance or mixture of substances 
under equilibrium conditions is the fact that the substance or 
mixture can undergo two exactly opposite changes : and that the 
opposing tendencies are equal. In order to acquaint the student 
with this, we shall present several examples beginning with a sim- 



Chapter II 



29 



p]e self-evident case, and follow it with gradually more complex 
cases. 

16. First Illustration of Equilibrium: — The Relation Between the 
Tendency of a Substance to Change to Vapor and the Reverse 
Tendency to Condense — Illustrated with Water and Steam. 

Experiment. — Secure a water bath or similar vessels of about 2 liters 
(2 quarts) capacity, and two round-bottom flasks of about 150 to 200 
c.c. capacity — which will fit side by side into the water bath. Place a 
l"x3" strip of wood across the water bath and bore two holes in it large 
enough to fit the necks of the flasks, rip the plank along the line of 
centers of the holes, insert the necks of both flasks from the same side, 
and clamp or fasten the two halves of the plank by means of a piece of 
twine or wire, or by means of two screws driven into the one-inch edge. 




Put a one-hole rubber stopper into one flask, and a two-hole rubber 
stopper into the other. Bend a piece of 7 mm. bore glass tubing so as 
to fit with one end into the one -hole stopper in one flask, and with the 
other into one hole of the stopper in the other flask: — this tube should 
terminate at the "inside" end of the one-hole stopper, while extending 
nearly to the bottom of the other flask. Put a straight piece of glass 



30 Schoch: Ixteoductory Chemistry 

tubing, about four inches long, with one end through the second hole 
of the two-hole stopper, slip a 2-inch piece of small rubber tubing over 
the outer end of this straight glass tube, and clamp this with a screw 
clamp. Fill the flask on the left side of the diagram half full of dis- 
tilled water. Fill the bath about one-third full of tap water and add 
enough common salt to saturate it. Put the flasks into the bath, and 
the latter on a tripod, and heat it to boiling. Keep the pinch clamp 
off the rubber tubing until a vigorous jet of steam issues* from the open 
end of the rubber tube: — then close this with a screw clamp. What be- 
comes of the steam now? Is there none formed now — that is, is the 
water in the flask boiling? Why not? At most, it will form steam 
bubbles slowly. Take the flasks out and pour a little cold water over 
the outside flask: — note whether or not the water is now boiling in the 
flask. Why! 

To describe this fact in technical terms, we say that we are 
confronted here with opposing tendencies — that of the liquid tend- 
ing to change the vapor, and that of the vapor tending to change 
to the liquid form. Concerning these tendencies, we know that 
at any fixed temperature — 100° C. in this case — the tendency of 
a liquid to vaporize is constant, but the tendency of its vapor to 
condense varies with its own concentration — or pressure: at 100° 
C. a concentration which drives an aqueous vapor pressure of 1 
atmosphere (or enough to support a column of mercury 760 
mm. in length at C C. ) has a condensing tendency just equal to 
the vaporizing tendency of water at the same temperature, and 
hence these two forces are in equilibrium. If the concentration 
of the aqueous vapor is lc^s than that corresponding to a pressure 
of 1 atmosphere, the tendency for the water to vaporize will be 
greater than the opposing tendency of the vapor, and the water 
will change to vapor: vice versa, if the concentration of the vapor 
is greater, vapor will condeflse to liquid. 

It is seen from the foregoing that the conditions of equilibrium 
between water and aqueous vapor at any one temperature are com- 
pletely expressed by stating the pressure of the aqueous vapor 
formed from water at each temperature. A complete table of 
these equilibrium conditions is ^iven in the Appendix (see Table 
of "Yapor Pressure of "Water"). 

The general relations here shown with water exist with every 
liquid (and even solid) that "vaporizes" appreciably. 

Questions on Chapter U. 

1. TVith what elements does oxygen combine? Is heat given 
out in all these reactions ? Do all compounds of oxygen liberate 
oxygen appreciably at sufficiently high temperatures ? 

2. Mention rive substances that give up oxygen. Calculate 
the per cents of their weights obtainable as oxygen gas at suffi- 
ciently high temperatures. 

3. TVhat is the weight of the resulting oxide produced by 



Chapter II 31 

burning 5 grams of sodium? of sulphur? of carbon? of phos- 
phorus? What is hydration? How much water is required to 
hydrate 5 grams of sodium oxide? of carbon dioxide? of sulphur 
dioxide? of phosphorus pentoxide? 

4. By what means — -in general— may the velocities of chemical 
changes be increased? Where do the forces reside that cause 
chemical changes? 



32 Schoch: Introductory Chemistry 



CHAPTER III. 

SIMPLE REACTIONS BETWEEN METALS AND ACIDS AND 

THE PREPARATION AND PROPERTIES OF 

HYDROGEN. 

1. The Reactivity of Different Metals. 

The first kind of a chemical reaction brought before the stu- 
dent consisted of the decomposition of a single substance, or the 
combination of two substances into a single substance, — which 
is the simplest sort of a change that can be found. The second 
kind of a chemical change to be brought before the student pre- 
sents the interaction of two substances which result in two other 
substances. For illustration, we have chosen the interaction of 
some metals with some acids, which results in the liberation of 
hydrogen from the acid, and in the formation of a compound of 
the metal together with the other components of the acid (i. e.. 
other than the liberated hydrogen). In general the equations for 
these changes have the form : 

M+HA=MA+H 

Here M stands for any of the metals which react thus. HA 
is used to denote the acid, because in this connection acids may 
be considered to be made up of only two different components, — 
hydrogen — H — being one of them, and all the remainder — A — 
being the other. The latter is frequently called the acid radicle. 

Experiment. — Put some copper filings into a test-tube and cover them 
with dilute hydrochloric acid : do the same with cadmium, zinc, tin or 
lead, and magnesium. Compare the rates of formation of the gas (hy- 
drogen) in these mixtures. Try the accelerating effect of a rise in tem- 
perature upon those mixtures which otherwise react slowly. Arrange the 
metals in the order of their reactivity with this acid. 

In the same way try the same metals with dilute acetic acid, and 
again with dilute sulphuric acid. Does the order of the reactivity of 
these metals remain the same with each of these acids? 

When all the common metals are arranged in the order of their 
tendencies to react with the same substances — to form the com- 
mon compounds such as oxides, chlorides, sulphates, nitrates, etc. — 
the following list is obtained : 

potassium 

sodium 

calcium 

magnesium 

aluminium 

zinc 

iron 



Chaptee III 



33 



cadmium 

tin 

nickel 

lead 

hydrogen 

copper 

silver 

mercury 

gold 

platinum 

The marked differences in the tendencies to reaction exhibited 
by these metals illustrates strikingly the fundamental fact that 
substances are impelled to reaction by tendencies inherent within 
them. 

The quantitative relations in the above reactions are expressed 
as follows:* 



Cd 
cadmium 
Zn 
zinc 


+ 
+ 


2HC1 

hydrochloric acic 

2HC1 


=, CdCl 2 + 

cadmium chloride 
= ZnCl 2 + 
zinc chloride ~ 


H 2 

hydrogen 

H 2 


Mg 

aagnesium 

Cd 


+ 

L 

+ 


2HC1 

2H(C 2 H,0 2 ) 
acetic acid 


MgCl 2 + 
magnesium chloride 

= Cd(C,H,0 1 ) 1 + 
cadmium acetate 


H 2 
H 2 


Zn 


_L 


2H(C 2 H 3 2 ) 


= Zn(C 2 H 8 2 ) 2 + 
name? 


H 2 


Mg 


+ 


2H(C 2 H 3 2 ) 


= Mg(C 2 H 3 2 ) 2 + 
name? 


H 2 


Cd 

Zn 

Mg 

2A1 


+ 
+ 


H 2 S0 4 
sulphuric acid 
H 2 S0 4 
H 2 S0 4 
6HC1 


= CdS0 4 + 
cadmium sulphate 

= ZnS0 4 +. 
= MgS0 4 + 
= 2A1C1 3 + 


H 2 

H 2 

H 2 

3H 2 


2A1 
2A1 


+ 
+ 


6H(C 2 H 3 2 ) 
3H,S0 4 


--= 2A1(C 2 H 3 2 ) 3 + 
= A1 2 (S0 4 ) 3 + 


3H 2 
3H 2 



The number of hydrogen atoms that an atom of metal "dis- 
places" is a measure of its combining power and is known as its 
valence. It is a definite number for each particular kind of metal. 
The equations above show that the valence of cadmium is 2; so is 
that of zinc and of magnesium; but the valence of aluminium is 
3. A more extensive consideration of valence is given in Chap- 
ter VI. 

*The molecule of hydrogen, just like that of oxygen and of most ele- 
mentary gases, has two atoms in each molecule. 



34 S ffOCH: INTRODUCTOIIT' CHEMISTRY 

2. The General Facts Concerning the Interactions of all Metals 

with all Acids. 

When the reaction is of the simplest sort — as with the acids 
used above — then only the metals above copper in the list above 
undergo reaction, while copper and the metals below it in the 
list have too small a tendency to effect a reaction. But with 
nitric acid and with concentrated sulphuric acid (in general, 
with acids capable of oxidizing action), all metals react except 
the lowest in the list — gold and platinum. However, with the 
latter acids the reactions are more complex than with the acids 
used above: hydrogen is not liberated, and instead other | 
nets are formed. Reaction- with these acids will be studied 
specially later on under the heading of "oxidation and reduction 
reaction-."' 

Experiment. — For the purpose of showing merely that nitric acid and 
concentrated sulphuric acid react and give products other than hydrogen, 
treat in different te>t-tubes a small piece of copper with nitric acid and 
a small piece of zinc with concentrated sulphuric acid. 

The foregoing facts, formula 3 , and equal a - old be com- 
mitted accurately to memory. The student should al>o drill him- 
self in working numerical problems similar to the f 
How many trains of zinc are required to produce 3 grams 

- How many LTams of pure sulphuric acid are re- 
quired to react with 5 grams of aluminium? How manv grams 
magnesium chloride ran be obtained with 10 srrar: .« g sium? 

3. The Preparation and Collection of Hydrogen and a Demonstra- 

tion of Some of Its Properties: a Practical Application of the 
Reactions Between Metals and Acids. 

Experiment. — Two students may work together on this experiment. 
Fit a 400-600 e.c. flask with a two-hole stopper ( rubber i. a long 
funnel, and a delivery tul>e as in Fig. A. Put a handful of gram; 
zinc into the flask, cover this with water and connect up the apparatus. 
Secure a water ba^in. three wide-month bottles and glass covers. Add 
small portions of concentrated hydror-hloric acid to the flask through the 
long-stem funnel until a brisk formation of hydrogen occurs. Allow the 
gas to escape until the air has probably been swept out of the flask, 
then fill the three bottles with the gas. and place them mouth downward 
on the glass slides. 

After filling these three bottles, attach a glass "•nozzle" to the delivery 
tube, light the issuing gas jet. and let the flame burn below a large 
beaker or flask filled with cold water: the condensed water is due to the 
reaction — 

2H.-<V=2H 1 

Reduce the size of the flame of one of the gas burners, and then lower 
one of the bottles of hydrogen down over the flame — to ascertain if the 
gas flame continues to burn in the hydrogen. 

Pour hydrogen from a bottle upward into another bottle filled with 
air and held mouth downward to catch the hydrogen | see Fig. B « . 



Chapter III 



35 



with a flame to ascertain if the gas has passed from the lower to the 
upper bottle. 

The hydrogen in the third bottle is to be mixed with approximately 




Fig. A. 

one-half its volume of oxygen, and the mixture to be exploded — for this 
purpose secure a suitable 'bottle full of oxygen, place the hydrogen bottle 




Fig. B. 

mouth downward over the oxygen bottle, remove the glass covers, invert 
the bottles together to hasten the mixing of the gases and then ignite 
the mixture. 



*b* 



Correct heating. 



Decant a small portion of the spent liquor from the generating flask 
into a small evaporating dish, put this dish on an iron ring-stand with 
a piece of asbestos board under it, and evaporate the liquid by heating 
it moderatelv with a Bunsen burner. 



36 



Schoch : Intboductoby Chemistry 



Do the same with 1 c.c. of dilute hydrochloric acid. Xote that the 
latter leaves no solid residue, while the former leaves a residue. Infer 
what the residue is. 

In your note book make suitable entries of the observation 
made in this experiment. Xote that incidentally the experiments 
have indicated something concerning the solubility of the gi a 
water, — its specific gravity, — color, and odor. 

4. Determination of the Relative Amount of Hydrogen Formed by 
the Simple Interaction Between an Acid and a Metal (Zinc 
and Hydrochloric Acid). 

Experiment. — Secure a bottle of one to two liters capacity, "narrow 
mouth"; e. g., a bottle in which acids and ammonia are ordinarily sup- 
plied in commerce. Fit it with a two-hole rubber stopper. Secure a 7 
mm. bore glass tube of such length that it may extend to the bottom of 
this bottle, and about 6 inches outside: bend the tube so that the out- 
side end will form an angle of 45° with the other end. Secure another 
piece of glass tubing, about eight inches in length, bend at the mid- 
point also to form an angle of 45°, and insert one end into the two-hole 
stopper so that it will terminate inside of the bottle just below the stop- 
per. To the other end of this shorter tube, fit a one-hole rubber stopper 
which fits a specially wide test-tube to be secured for this purpose. 




The outside end of the other glass tube — that is. the one which ex- 
tends to the bottom of the bottle — is to be fitted with about ten to 
twelve inches of small pliable rubber tubing, and the other end of this 
tubing is to have a small glass nozzle attached to it. A pinch clamp 
is put on the rubber tube. 

Weigh out accurately about 1 gram of pure zinc, and place this in the 
bottom of the large test-tube. Then secure a short, small test-tube, and 



Chapter III 37 

put into it about 10 c.c. of concentratel hydrochloric acid plus an equal 
volume of distilled water. Add one drop of a copper sulphate solution: 
this is for the purpose of producing a trace of copper metal on the 
zinc — which will "catalyze" the action between the zinc and the acid. 

Lower the small test-tube carefully into the large test-tube (after in- 
serting the zinc in the latter ! ) . Fill the large bottle two-thirds full of 
tap water, insert tightly the stopper with the glass tubes, drain the 
water through the nozzle until the rubber tube and nozzle are full of 
water, then close the pinch clamp on the rubber tube. Fit the large 
test-tube with its contents securely to the one-hole rubber stopper on the 
connecting glass tube. Secure a large (600 c.c.) beaker, put a small 
amount of tap water into it. Then put the end of the nozzle under the 
surface of this water, open the pinch clamp and raise the beaker until 
the levels of the water in the beaker and in the bottle are at the same 
height. After holding the beaker there long enough for the pressure of 
the gas in the bottle to become equal to the atmospheric pressure, close 
the pinch clamp, pour out all the water in the beaker, put the nozzle 
again into the beaker, open the pinch clamp and slip it aside so that it 
will hang on the rubber tubing without clamping the latter. 

Next tilt the bottle in order to allow most of the acid to run out into 
the wide test-tube and hence come in contact with the zinc. Then set it 
straight up, and allow the action to proceed, being careful to catch all 
the expelled water in the beaker. 

When the zinc has been consumed, raise or lower the beaker to make 
the pressure inside of the bottle equal to the atmospheric pressure, close 
the rubber tube with the pinch clamp, and weigh the beaker and water 
on a coarse or platform balance — to the nearest whole gram. Then pour 
out the water and weigh the empty beaker. 

Ask the instructor to read the barometer. Take the temperature of 
the water remaining in the large bottle. 

Calculations. — The net weight in grams of the water is the same as 
the number of cubic centimeters of hydrogen obtained (fundamental fact 
of metric system ! ) The gas was collected over water, at the observed 
temperature (of the water), and under the observed atmospheric pres- 
sure: put your observed results in the note book thus — " — c.c. of hydro- 
gen at — ° C. and under — mm. pressure, saturated with moisture." 
Calculate what volume of hydrogen this would be if dry at 0° C. and 
under 760 mm. (see Chapter IV. Art. 4). Next calculate how many c.c. 
of dry hydrogen at 0° C. and 1 atmosphere would have been obtained 
from one gram — atom of zinc (65.37 grams!). 

Next calculate how many grams of hydrogen the latter volume would 
weigh (see weight of 1 liter below). 

5. Other Properties of Hydrogen. 

When hydrogen and undiluted oxygen are mixed in a suitable 
burner in the ratio, by volume, of 2:1, a very hot flame is ob- 
tained. When mixed and kept at or below room temperature, no 
perceptible reaction takes place. If the mixture is kept at 300° 
C. for several days, a very small amount of reaction will take 
place. At 518° C. several hours are required for complete reac- 
tion, but at 700° C, and above, reaction is almost instantaneous. 
When the mixture is kept at very high temperatures (2000° C. 
and above) equilibrium is reached while some of the oxygen and 
hydrogen are still un combined. 

Finely divided platinum, palladium, iron, and iron oxide 



38 S hoch: Introductory Chemistry 

"catalyze*' the reaction between hydrogen and oxygen — so that 
the latter will combine fairly rapidly even at ordinary tempera- 
tures when in contact with one of these "catalyzers." 

A liter of hydrogen at 0° C. and 760 mm. weighs only 0.£ 
grams. It is the lightest of all known gases. Air is 14.5 times 
as heavy. Hydrogen lias been liquefied (boiling point. — 21 
C.) and solidified (melting point — 260° C). Hydrogen is ab- 
sorbed by many metals (platinum, palladium, iron, gold) and this 
action explains the catalytic effect that these metals have 
mixtures of hydrogen and oxygen. 

Questions on Chapter III. 

1. Xame several metals any one of which when put in 

tact with any on- - ral acids — also to be named — react bo 

as t<» give hvdrogen and a compound of the metal with the com- 
ponents of the acid other than the hydrogen. How many grams 
of each of the metals named are required to produce 5 gram- of 
hydrogen? How many grama of each of the acids are required 
to produce 5 grams of hydrogen ? It is understood that the wat^r 
with which the acids are mixed (in which they are dissolved) is 
not to be included in the weights. 

2. State the general facts concerning the interaction ol 
metals with all acids. 

3. State the properties of hydrogen which were demonstrated 
experimentally before you. 



Chapter TV 39 



CHAPTER IV. 

THE MOLECULAR-KINETIC STRUCTURE OF GASES AND OF 
CONDENSED FORMS (LIQUIDS AND SOLIDS). 

1. Introduction. 

The chemical and physical study of substances in their three 
different forms have revealed that the gaseous form is not only 
the simplest in structure and behavior, but that the molecular 
structure and most properties of all gases are exactly the same. 
Hence, we shall consider gases first. 

2. The Structure of Gases. 

A gas consists of small particles (molecules) separated by rela- 
tively wide, empty spaces. The molecules are constantly moving, 
rapidly, in straight lines and change direction merely whenever 
they hit other molecules or some solid or liquid obstruction. This 
constant motion or flight of gaseous molecules is the cause of the 
rapid diffusion or spreading of unconfined gases through unoccu- 
pied space, — hence, also the cause of their diffusing into other 
gases (because the greater part of a gas volume is not equipped 
by molecules). 

Experiment. — Demonstration of the Diffusion of Gases. (To-be per- 
formed by the instructor.) 

We shall employ hydrogen and air to demonstrate the diffusing 
tendency of gases. Since the mass of the hydrogen molecule (H 2 ) 
is only 2 atomic weight units, while that of the nitrogen (which 
is 80 per cent of the air) has a molecular mass of 28, it follows 
that, at the same temperature, their molecular velocities have the 
relation (see Article 3a) — 

i(2)v 2 hydr =i(28)u ? nitr . or 

N2 

Hence, if we put hydrogen and nitrogen at opposite ends of a 
tube, 3.7 times as much hydrogen as nitrogen will pass through 
during the same time. 

For our tubes we shall employ the pores in a 1 quart porous 
earthenware "battery jar" (see A in accompanying figure). This 
is closed securely with a rubber stopper, and connected with bot- 
tles B and C by means of glass tubes — as shown. B is filled with 
colored water. F is a large iron ring support, and G is a plank 
with a small hole drilled in the center. E is a piece of card- 
board perforated to fit A. D is a large beaker of a bell jar, which 



40 



Schoch: Introductory Chemistry 



has been filled with hydrogen over water, and is then transferred 
(with the aid of pane of glass). 

E is pushed down with the bell jar on it. Immediately, the 
colored liquid in B will be blown over into C. and some" of it 
blown out of C, through the nozzle. T\lien the pressure has spent 




itself, the bell jar is removed : the liquid will then be drawn from 
C back into B. 

The cause of the pressure and suction is the difference in the 
velocities of the molecules of hydrogen and air. resDectivelv. With 



Chaptee IV 41 

this suggestion, the student should be able to explain the actions 
in the experiment. 

3. Quantitative Relations in the Behavior of Gases. 

(a) At the same temperature, the velocities of zig-zag flight 
(vibration) of the molecules of different gases are such as to give 
to the molecule of each gas the same average 'kinetic energy 
(i m v 2 ). 

(b) At the same temperature, and under the same pressure, 
equal volumes of all gases contain the same number of molecules. 
(Avogadro's Law.) This number is 2705X(10) 16 molecules in 
1 c.c. at 0° C. and 760 mm. pressure. 

(c) If the effluent tube of an automobile air pump is closed, 
and the piston is forced down half way from the top, then all the 
molecules which at first occupied the whole pump cylinder will be 
confined in half the volume: — a little thought will reveal that 
each molecule now has only half as far to travel to hit the piston 
head, and hence it will make twice as many hits per second than 
it did when the piston head was at the top; and the pressure on 
the piston head is twice as great as it was when the piston head 
was at the top. This relation between the volume and the pres- 
sure of a gas is perfectly general, and is expressed thus (at the 
same temperature) the pressure of a definite amount of gas varies 
inversely with its volume (or vice versa). This is known as the 
Law of Boyle. - 

(d) When a gas has its temperature raised (or lowered), then 
the velocity of flight of its molecules is increased (or decreased) 
to exactly such an extent as to change either the volume "v" only 

T, 

— or the pressure "p" only — or their product (pv) — by , 

t, ' 

where T x denotes the original temperature (measured on the 
Absolute Scale) and T 2 the final temperature. This is known as 
the Law of Charles. The Absolute Scale reading is derived from 
the centigrade scale reading by adding .273.1° to the latter. 

4. The Reduction of Gas Volumes to Standard Conditions. 

The Laws of Boyle and Charles make it possible to find, by cal- 
culation, the volume occupied by a gas under any desired condi- 
tion of temperature and pressure if its volume at one temperature 
and pressure is known. For example, if we have 50 c.c. of a 
(dry) gas at 26° C. and 750 mm., and we wish to know what vol- 
ume this amount of gas will occupy at — 10° C. and 710 mm., 
Ave proceed as follows : We can calculate the effect of either in- 
fluence first — let us take the pressure first: The gas changes 



42 Schoch: Introductory Chemistry 

from a greater to a lesser pressure — hence it will expand — and 
we must multiply by an improper fraction formed from the two 

750 750 

pressures — that is, by , which we indicate bv 50 V 

710 710 

750 

The volume of the eras now is (50X )< and tin- temperature 

710 

effect on this volume is obtained, as follows: The change will 
cool the gas and lessen the volume, — hence we must multiply by 
a proper fraction formed by the two temperatures — that is. by 

273+ (—10) 263 750 263 
= and we obtain (50X ) X 

373+26 209 710 299 

Frequently gases are collected and measured "over water'*; 
that is, saturated with water vapor: and it is desired to know 
what volume they will occupy wken dry. To calculate thia re- 
duction in volume, we make use of the fact that liquids evaporate 
into spaces occupied by other vapors or gases as though the 
gaseous space were a vacuum. Thus, when oxygen, or hydrogen, 
is collected over water at 26 c ('.. aqueous vapor will be mixed 
with the oxygen or hydrogen to such an extent that the aqueous 
vapor alone would produce a pressure of 25 mm. (see Appendix, 
Table of "Vapor Pressures of Wattr"). 

Now, if the aqueous vapor molecules are producing — or sup- 
porting — 25 mm. pressure, then the oxygen molecules are sup- 
porting only the remaining part of the pressure. If the total 
pressure is 750 mm., then the oxygen is really only under 725 
mm. pressure, and hence 725 instead of 750 would be used in 
making any further calculations as per example above. 

Problem: Calculate what volume 25 c.c. of air collected over 
water at 20° C. and 740 mm. would occupy dry, at 0°, and 
760 mm. 

5. The Condensation of Gases to Liquids. 

Xothing was said in the foregoing about an attracting force 
acting between the molecules of gases, yet such forces are always 
present and frequently quite effective. However, they are effec- 
tive only through very small distances — i. e.. the attractive forces 
between two molecules is appreciable only during the time that 
they are very close together. With such gases as hydrogen, 
oxygen, nitrogen, etc., under atmospheric pressure (or less) and 
at room temperature (or above), the attractive forces between 
the molecules do not affect the behavior of the gases appreciably. 



Chapter IV 43 

But if the molecules of these gases are brought closer together, 
particularly at temperatures far below 0° C, at which the veloci- 
ties of the molecules are greatly reduced, theu the attractive 
forces affect the behavior of even these gases. With sufficient 
compression, or lowering of temperature (or both), the attract- 
ing forces will become sufficiently extensive to retard the mole- 
cules in their flight and to hold them together — then the gases 
are liquefied. 

It must not be thought, however, that the molecules lose all 
their kinetic energy when a gas is liquefied: they lose a part 
which appears in the "latent heat" of condensation, but they re- 
tain the greater part of their energy of motion and continue to 
move — though only in close contact with other molecules. 

A little reflection will reveal that all the molecules of a sub- 
stance cannot have exactly the same velocity because collisions 
change the velocities of the colliding molecules (which is illus- 
trated in the collision of billiard balls), and the velocity we or- 
dinarily speak of is an average velocity possessed very nearly by 
most molecules. Hence, in the surface of every liquid there will 
be some molecules which through collisions receive sufficiently 
great velocities to overcome the attractive forces of the other 
molecules, and to fly into the gaseous space above. As long as 
they are there sufficiently far away from other molecules of their 
kind, these "vaporized" molecules will remain in the gaseous 
space; but since some of them will collide with some of their own 
kind, some of the "vapor" will be condensed. The number of 
molecules thus condensed will become larger as the number of 
molecules in the vapor becomes larger, until finally the number 
condensed will be equal to the number vaporized in the same 
space of time: then we have equilibrium. Thus equilibrium is 
seen to be the result of two oppositely directed changes taking 
place at the same rate. 

It is seen from the foregoing that molecules of liquids are close 
together — they practically touch each other; and the molecules 
hold together by mutual attraction. However, since every mole- 
cule is entirely surrounded by molecules of its own kind, it ex- 
periences no restraint from this molecular attraction because the 
attractions on opposite sides balance each other. Since their 
straight line flight is confined to very short distances, their mo- 
tion may be properly called "vibration": yet, through the recoil 
at different angles — experienced in their "vibrations" — they slowly 
move through the mass of the liquid in all directions. 

6. The Vibration of Atoms Within the Molecule. 

Although the atoms constituting a molecule are held together 
securely by their mutual attraction, yet the behavior of substances 
indicates that the atoms in a molecule are not rigidly fixed with 



■^ 3 HOCH' IXTEODUCTOEY ChEMISTEY 

reference to each other, and that they are moving to and fro within 
a limited space. Jnst like the '"'vibratory'" motion of molecule?, 
so this vibratory motion of the atoms also is increased bv a ria 
temperature and hence a gradually increasing number of them will 
attain such high velocities as to fly beyond the confines of the mole- 
cule they are in: this phenomenon, known as disc g quite 
general, but is observed with only a few substances at ordinary 
room temperatures, and does not affect many substances appreciably 
even at high temperatures. Thus steam is dissociated onr 
of one per cent at 1500° C. and only about 1 per cent a- i 
Substance with high melting p~ _-.. most rocks and minerals, 
-eadily dissociated than gase-. so that in most cases 
the dissociation does not become noticeable: this is 
cause the products formed tend to react in the reverse sense, and 
mere traces of the products are enough to stop further dissocia- 
tion, i. e., they produce equilibrium. The part that such slight 
dissociation plays in chemical reactions is considered and illustrated 
in the next chapter. 

7. The Solidification of Liquids: Amorphous and Crystalline 
Solids. 

When liquids have their temperatures reduced, the "vibratory" 
motion of their molecules gradually beeon. - s, the attractive 
s become more effective, and the mass as a whole becomes 
more viscous. This is strikingly illustrated in the cooling of 
molasses, and of pitch : when cold, these materials have the ap- 
pearance -. but, in reality, they are merely extremely vis- 
cous liquids. Since they have no particular geometric form, they 
are called amorphous sol 

Many other liquids behave quite differently on cooling: long 
before they become appreciably more viscous, they begin to form 
pieces with specific geometric forms — that is, forms having defi- 
nite angles between the planes. With pure liquids, this forma- 
tion of crystals tai at sharply defined temperatures. Thus 
water freezes The change is accompanied with the liber- 
ation of heat, which is due to the fact that the crystallized mole- 
cules have given up a large part of their molecular f and 
remain almost (not quite) motionless in the place within the 
crystal which they have taken. 

This sudden arr - . J molecules takes place only when mole- 
cules have had time and opportunity to place themselves in an 
orderly manner besides others of their own kind, similar to bricks 
in a wall. Such regular internal •'•'structure" is characteristic of 
crystals, and differentiates them from amorphous solids. Another 
characteristic of crvstals is the sudden transition from hard crys- 
tals to limpid liquid, at a sharply defined temperature. — while 



Chapter IV 45 

amorphous liquids soften gradually through a long range of tem- 
perature. 

8. Dissolved Substances: Solutions. 

Everybody is familiar with the fact that liquids wet solids, — . 
which shows that there is a direct attraction between the mole- 
cules of the liquid and the solid. In many cases this attractive 
force succeeds in dislodging single molecules or larger particles 
from a solid and surrounding them completely with molecules of 
the liquid : such a resulting aggregate is called a solution. If, in 
this action, the liquid separates the solid into single molecules, 
then the solution is a true solution; but, if the particles are com- 
posed of several or many molecules, the solution is known as a 
colloidal solution, — and the dissolved substance is called a colloid. 
Ink and liquid glue are familiar examples of colloidal solutions, 
wliile sugar-water and salt-water are examples of true solutions. 

In ordinary dilute solutions, the particles of dissolved material 
(called solute) are relatively as far apart from each other as the 
molecules of moderately compressed gases, — hence they do not at- 
tract or affect each other to any grea.t extent, and, furthermore, 
this attraction is balanced on all sides and thus neutralized. The 
solvent molecules also do not affect them because they surround 
the solute molecules completely and the molecules on opposite sides 
neutralize each others' "pull." Hence, within the body of the 
solution, there is nothing that restrains the motion of the solute 
molecules, and they move freely in accordance with the kinetic or 
temperature impulse. 

Since the free space in liquids is extremely small, the solute- 
molecules are colliding rapidly with other molecules and their 
main motion is a sort of vibration, yet in addition to this they 
move slowly through the liquid in all possible directions. The 
latter slow motion is called diffusion. 

9. Boiling Points, Freezing Points, and Osmotic Pressures of Solu- 

tions. 

Solutions of solids have boiling points higher than those of 
their pure solvents : a saturated solution of common salt (sodium 
chloride) boils at 108.8° C. The rise increases with the relative 
amount of salt contained in the solution. 

Solutions of solids have vapor pressures lower than those of their 
pure solvents at the same temperature. If a pan of pure water, 
and a solution of common salt are placed under the same bell jar, 
the pure water will gradually evaporate and be condensed into the 
salt solution because the gaseous space will be filled with vapor 
from the pure water at a pressure greater than that exerted by 
the salt solution, and hence water will be condensed in the latter 
until all the pure water has vaporized. 



46 Schoch: Introductory Chemistry 

Some substances are so extremely soluble as to form a solution 
on their surface whenever sufficient aqueous vapor is in the air 
around them. The action is identical with that in the "bell jar" 
illustration above. This phenomenon is frequently observed with 
candy exposed to the air. Substances which have this property 
are said to be "hygroscopic" or to "deliquesce." 

The boiling points of solutions of gases or liquids in (other) 
liquids may be either higher or lower than those of the pure solv- 
ents: they show all possible relations, and each mixture must be 
studied by itself. The same is true of their vapor pressures when 
compared at the same temperature. 

The freezing points of solutions are lower than those of their 
pure solvents : a saturated solution of common salt in water freezes 
at —22° C. 

When a solution (e. g., of sugar in water) is put inside of a 
bag of certain animal or vegetable tissues, such as fish bladders, 
parchment paper etc., and the whole bag is immersed in the pure 
solvent (e. g., water), the latter will be drawn into the bag. The 
material of the bag has no noticeable pores or holes in it: it -im- 
ply "soaks up" water on one side and gives it up again to tin 1 solu- 
tion on the other side. Looked at from the outside, the phenom" 
enon appears to he actuated by the solute tending to spread into a 
larger volume of solvent: the force which appears to be impelling 
the solute to attain a large volume i- called osmotic pressure. 

10. Compounds of Solvent with Solute. 

When "commercial'" soda-ash (composition, Na 2 < '()..) is dis- 
solved in water until a saturated solution is obtained, and the lat- 
ter is then allowed to evaporate, crystals will be obtained which 
when heated will give up a great deal of water: their composition 
is expressed by the formula Xa_,( '()... 10H 2 O. The ten molecules 
of water thus united with every molecule of Xa.,00. are called 
water of crystallization. The crystals of many salts contain defi- 
nite numbers of molecules of water, the numbers ranging from 
one to twelve. 

There is evidence which shows that even in solution many solute 
molecules have "water of crystallization" combined with them, 
but we do not ordinarily become aware of thi? combination. 

Since crystals containing water of crystallization are definite 
chemical compounds, they form a vapor with definite equilibrium 
pressure at each temperature — just as pure water (see Chapter II, 
Art. 16) or any other single, pure substance does. Although the 
vapor from these crystals is composed of water only, yet this is 
sufficient to hold the equilibrium with the crystals as long as some 
of the dry, solid material necessary to complete the composition is 
present — mixed with the crystals. 

If crvstals which contain water of crvstallization are in contact 



Chapter IV 47 

with air containing less water vapor than that corresponding to 
the crystals' vapor pressure, the crystals will lose water and break 
up, forming a fine powder: they are said to "effloresce." This is 
strikingly illustrated by soda crystals (sal soda or, washing soda, 
Na 2 CO, 10H. 2 O), which, during dry weather, change to a white 
powder. 

11. Second Example of Equilibrium: The Dissolution of a Solid in 
Water Illustrated with a Determination of the Solubility of 
Potassium Nitrate. 

Secure about 25 grams of potassium nitrate, and crush it as fine as 
possible in a clean dry mortar. Put the powder into a folded piece of 
paper and from this pour it into a small flask. Add about 30 c.c. of dis- 
tilled water, stopper the flask with a clean cork, and shake it fairly vig- 
orously for at least five minutes. A part of the crystalline material 
should remain in solid form. Secure a thermometer and note the tem- 
perature of the solution. 

Then secure a clean burette and a clamp to fasten it on the iron ring- 
stand, pour the solution just prepared into the burette, being careful to 
fill the nozzle by running some of the solution back into the flask and 
then pouring this again into the burette, always retaining the undis- 
solved crystals in the flask. For directions concerning the "reading of 
the burette," see figure, Chapter VI, Art. 2. Then secure a small evap- 
orating dish, clean, dry, and weigh it accurately, and note the weight on 
a slip of paper. Then pour about 15 c.c. of the solution into the dish, 
and note the amount taken. Weigh the dish and contents promptly and 
then place the dish and contents on top of a hot water bath for gentle 
evaporation. 

While the solution is evaporating, proceed with some other experiment. 
When the content of the dish is dry, wipe the outside of the dish clean, 
and weigh the dish and contents. Subtract the weight of the empty dish 
and thus secure the weight of the salt in the amount of solution taken. 
Calculate the amount of salt in 100 c.c. of solution saturated at the ob- 
served temperature. Subtract the weight of the salt from the weight of 
the solution, thus finding the weight of water which dissolved the weight 
of salt obtained at the observed temperature. 

Calculate the amount of salt dissolved by 100 c.c. of pure water. 
Also calculate the weight of 1 c.c. of solution : — this is the specific 
gravity of the solution at the temperature at which it was meas- 
ured. Put all of the numerical results and calculations into 
your note book. 

Compare your numerical results with those obtained by other 
members of the class. 

Put the remainder of the solution back into the flask with the remain- 
ing crystals, place the flask on a wire gauze on the ring-stand, heat it 
and shake it at intervals. Note that this salt is much more soluble in 
hot water than in cold water. Set the flask and contents aside to cool — 
or, if necessary, hasten the cooling by allowing cold tap-water to run 
over the outside of the flask; some of the salt will crystallize out as 
the solution cools, and when the solution has cooled to the former tem- 
perature, it will contain only as much of the salt as it held before it 
was warmed. To avoid wasting this "fairly expensive" salt, return the 
crystals and remaining solution to the instructor. 

We may consider that this experiment reveals the action of two 



48 Schoch: Introductory Chemistry 

oppositely directed tendencies : — one is the dissolving tendency of 
the crystals ; the other is the tendency of the dissolved salt to sep- 
arate from the solution. Except for the presence of solvent here, 
this phenomenon resembles that shown in our first example of 
equilibrium, — the crystals here taking the place of the water in 
the first example, and the dissolved material taking the place of 
the steam. 

Before discussing this phenomenon any further, we must intro- 
duce here a fundamental fact concerning the change of activity of 
a substance: — at constant temperature, the activity of any sub- 
stance depends on its concentration, and in most casos varies di- 
rectly with its concentration. 

The concentration of a substance is the weight of a given 
amount divided by the volume it occupies "uniformly." If the 
substance is in the gaseous or in the dissolved form, its vol- 
ume is that of the whole gas space, or solution space, because it 
extends uniformly into all these parts. If it is a solid (or a 
liquid), we must subtract the volume of any unfilled "recesses." 

Gases and dissolved substances can have their concentrations 
varied very extensively,?— accordingly the activity of a gas or of a 
dissolved substance may have greatly different values. 

Solids and liquids (not the dissolved substances) have practi- 
cally always the same concentrations at any particular tempera- 
ture, — hence at any one fixed temperature, their activities are 
practically always the same. 

With this information, we may now resume the discussion. Evi- 
dently, the crystals have a fixed activity or dissolving tendency at 
the temperature at which the solution was first prepared ; but the 
tendency of the dissolved portion to "form crystals''' increases with 
its concentration until the two are equal : then we have equili- 
brium. Crystals are then neither dissolved nor formed (or looked 
at in another way, just as much of the crystals is dissolved per 
second as is separated from the solution in the same time). 

The experiment also shows the effect of temperature upon this 
equilibrium: — it shows that, at higher temperatures, equilibrium 
require? more of the potassium nitrate to be present in the solu- 
tion. We say, technically: — the equilibrium has been shifted 
toward the ''solution" side, meaning thereby that relatively less of 
the potassium nitrate will remain as crystals. This shift is iden- 
tical in sense with the temperature shift of the first example of 
equilibrium. Why ? 

12. Relation Between Solubility and Temperature. 

The foregoing experiment showed an example in which the sol- 
ubility of the solid increases with temperatures. From our general 
experience in this world, we are likely to jump at the conclusion 



Chapter IV 



49 



iSOr 



140 




O 1CP 30° 50° 40" 5CT bO° 70° 80° 90° 100 9 



'JLl 



:■_: 



:: 



72 -_ 



Chapter V 51 



CHAPTER V. 



A REVERSIBLE CHEMICAL REACTION— THIRD ILLUSTRA- 
TION OF EQUILIBRIUM. 

1. Introduction. 

For the first two illustrations of equilibrium, we presented 
changes which are as simple as any that could be secured — the 
vaporization of a liquid, and the dissolution of a solid. These 
changes are usually spoken of as physical changes; but since the 
forces of nature are not limited, in their application, by the 
boundaries set by man between the domains of physics and chem- 
istry, these illustrations show the same relations and forces that 
are shown by strictly chemical changes. 

However, for the next, more complicated example, we shall 
present a purely chemical phenomenon. But before the equili- 
brium conditions can be considered, some of the experimental data 
must be presented separately. These data also are important on 
their own account. 

2. The Action of Metals on Water (Steam) — A Further Illustra- 

tion of the Different Reactivities of Metals, and of the Influ- 
ence of Temperature Upon Reaction Tendencies. 

The very reactive metals in the upper part of the list of metals 
in Chapter III are so reactive that they displace hydrogen from 
water. Those highest in the list (potassium, sodium, calcium) 
are so reactive that their rate of reaction with cold water even is 
quite rapid. 

Experiment. — (a) To demonstrate the foregoing remark, fuse up one 
end of a short piece of glass tubing, "pack" into the bottom of this tube 
some "clean" sodium. Then secure a clean porcelain dish, fill it with 
distilled water, drop into it a piece of red litmus paper, and invert in it 
a test-tube filled with water. Drop the "sodium" tube into the water, 
and place the mouth of the inverted test-tube right down upon the open 
end of the "sodium" tube, and collect the hydrogen. (If the sodium 
escapes to the top of the water, turn your face away from the dish until 
the sodium has been consumed.) Test the gas collected to see if it is 
combustible. 

The sodium and the water react according to the equation: 

2Na+2H 2 0=2NaOH+H 2 . 

Note that the litmus paper changes color. 

In your note book make suitable entries of all observations made in 
the experiments in this lesson. 

Metals slightly lower in the list than sodium — e. g., aluminium 
and magnesium — have a lesser reactivity: their rate of reaction 
with cold water is too small to be appreciable; but at a higher 



52 Schoch: Introductory Chemistry 

temperature — with hot water — they react rapidly enough for the 
change to be noticeable. 

Experiment. — (b) A 250 c.c. round-bottomed flask is fitted with a one- 
hole rubber stopper and a conducting tube of such length and bent so 
that the flask may be placed on a ring-stand to be heated and the gas 
formed may be collected over water, just as hydrogen and oxygen were 
collected in previous experiments. Care should be taken not to allow the 
conducting tube to extend beyond the rubber stopper inside of the flask. 
Put some finely divided magnesium into the flask and then fill the flask 
and conducting tube full of water. Also fill a test-tube with water and 
invert it in the collecting trough so as to have it ready for collecting the 
gas. 

Xote that as long as the water is cold, no action takes place. 

Heat the water gradually until it boils and collect the gas that passes 
over. Show that it is combustible. 

Evidently, the rise of temperature has increased the rate of action so 
that the reaction takes place appreciably at 100°. 

By using water in the form of steam, the reaction may be 
made to take place at still higher temperatures, and hence a 
greater velocity will be attained, so that even a metal with a re- 
activity no greater than that of iron will react rapidly enough 
for the change to be noticeable. 

Experiment. — (c) Secure a piece of "combustion tubing" about 50 
cm. in length, bend it near the center to an angle of 120 degrees, fit one 
end with a two-hole rubber stopper and two pieces of very narrow glass 
tubing, and the other end with a one-hole stopper and an ordinary piece 
of glass tubing. Secure the flask and fittings used as a hydrogen gener- 
ator above, but fill it half full with water, and use it to furnish steam. 
Instead of using — as shown in the figure — a single glass tube connecting 
the flask to the combustion tube, use txco short pieces of glass tubing, 
and connect them with a six-inch piece of rubber tubing. Put some finely 
divided metal (magnesium ribbon or fine iron filings) into the horizontal 
part of the tube, and connect up the apparatus as shown in accompany- 
ing figure. One of the tubes extending through the two-hole rubber stop- 
per into the combustion tube extends through the stopper at least 8-10 
cm., while the other terminates "flush" with the inner end of the stop- 
per: this tube enables the experimenter to remove any water condensed 
in the cold part of the combustion tube. 

Before connecting the boiler to the combustion tube heat the water 
until a steady stream of steam is obtained. Temporarily discontinue 
heating the water, but warm up the tube until it is hot enough not to 
condense steam; then connect the boiler to the tube, and start the steam 
cautiously through the tube, being careful to keep the tube hot enough 
not to condense steam, and also being careful to draw off through the 
extra tubing any water condensed in the lower part of the tube. When 
everything is in proper working order, heat the tube strongly at the point 
where the metal has been placed: when the proper temperature is reached 
the steam and the metal will react rapidly, and the hydrogen formed 
should be collected in the bottle inverted over the end of the delivery 
tube. Ascertain if the gas collected is combustible. 

3. The Reduction of Metallic Oxides: — The Reverse of the Pre- 
ceding Reaction. 

Xote. — The removal of oxygen from one of its compounds by the 
action of a third substance — as illustrated in the reaction in this 



Chapter V 



53 




54 Schoch: Inteoductoey Chemistey 

article — is called reduction. The latter term probably originated 
from the metallurgist's use of the term reduction to denote the 
extraction of metals from their ores: the ores "reduced" in fur- 
naces are generally oxides, and the chemical change consists in 
the removal of the oxygen by a gas. It is the reverse of oxida- 
tion. Besides being used in their primary senses, the terms oxi- 
dation and reduction are also used in more extended senses. The 
latter will be shown later on. 

As might be expected, those metals which have a greater tend- 
ency than others to form compounds, exert also a greater resist- 
ance to being changed back to the metallic form — they are said 
to be more difficult of "reduction." The position of the metals 
in the table given in Chapter III shows their relative ease or diffi- 
culty of reduction — the oxides of the metals in the lower part of 
the list are easily reduced, while the oxides of those in the upper 
part are hard to reduce. It is on this account that gold and 
platinum, which are the lowest in the list of metals in Chapter 
III, are always found in the earth as free metals ; mercury, silver, 
and copper are found sometimes as free metals and sometimes as 
compounds; but the metals farther up in the list are scarcely ever 
found free in the earth. Again on account of the relative ease or 
difficulty of reducing their ores (oxides!), the free metals first 
prepared and used extensively by man were gold and silver, next 
came copper and tin, then iron and zinc, and only recently alum- 
inum and magnesium. 

The molecular dissociation brought about by elevating the tem- 
perature, which was discussed in the preceding chapter, is directly 
responsible for bringing about reaction in the preceding experiment, 
and hence the latter serves to illustrate this point. When heated, 
metallic oxides dissociate slightly into free metal and free oxygen. 
The fraction dissociated is not sufficient to be noticeable because 
free metal and oxygen gas have a tendency to change backwards, 
and very small amounts of these two suffice to stop the "forward 
change." But when hydrogen gas is present, the free oxygen com- 
bines with hydrogen and removes the opposing tendency. Then 
more oxide dissociates; this, in turn, combines with hydrogen, 
and thus the change continues. 

Experiment. — Equip a flask for the preparation of hydrogen — as in 
the preceding experiment. Secure a piece of wide, hard glass tubing — so- 
called combustion tubing, — 30 c.c. in length. Fit cork stoppers into the 
ends, and perforate the stoppers to suit the connecting tubes shown in 
the accompanying figure. Secure a "porcelain boat," fill it with copper 
oxide and insert it into the combustion tube. The copper oxide could 
be put directly into the combustion tube, but the use of a boat facilitates 
the operation. Connect the apparatus as shown in the figure, and start 
the generation of the hydrogen. After the air has been expelled from 
the apparatus, begin to heat the portion of the tube in which the oxide 
has been placed. 

After the substance has been heated thoroughly in the current of 
hydrogen, allow the tube to cool, and then empty the substance into a 



Chapter V 55 

mortar; note that it has changed color. Try to grind it slightly in the 
mortar, and note the metallic streak obtained. 

Repeat this experiment with iron oxide in place of copper oxide. Test 
the original and the resulting solids with a magnet. 

4. The Determination of the Batio by Weight in Which Oxygen 

and Hydrogen Combine to Form Water. 

The reaction which has taken place in this experiment is the 
following : 

CuO+H 2 -Cu+H 2 0. 

If the boat filled with copper oxide had been weighed before 
placing it in the tube, and then again after removing it, the 
difference would have given the weight of the oxygen which has 
been combined with hydrogen to form water. If, furthermore, 
the water formed had been collected by passing it through a tube 
filled with a substance which absorbs the water only (e. g., cal- 
cined calcium chloride), then the weight of all the water formed 
with this weight of oxygen would have been obtained by weighing 
this "absorption tube" before and after the operation. This data 
would give the ratio by weight in which hydrogen and oxygen 
combined to form water. By these experimental means all the 
earliest determinations of this ratio were made — by Berzelius and 
Dulong in 1820, — by Dumas and Stas in 1843. The following 
example may serve to illustrate the details of the procedure: 

Weight of boat and contents before heating 15.184 grams. 

Weight of boat and contents after heating 14.531 grams. 

Difference, weight of oxygen 0.653 grams. 

Weight of calcium chloride tube before the experi- 
ment 36.252 grams. 

Weight of calcium chloride tube after the experi- 
ment 36.987 grams. 

Difference, weight of water formed 0.735 

Less weight of oxygen 0.653 

Difference, weight of hydrogen 0.082 

Ratio in which hydrogen and oxygen combine to form water: 
0.082 :0.653::1:8. 

This numerical value is one of the most important ones in 
chemistry; and the procedure of its determination should be 
learned accurately by every student in chemistry. 

5. The Equilibrium Between Iron Oxide, Hydrogen, Iron and 

Steam. 

The main subject of this chapter is now to be considered. It 
has been shown that hydrogen reduces iron oxide, and that steam 



:-: -:z::h Zyzz: it :-::-* "z:::: ; ' 



r up* 




^Q 



Chapter V 5? 

reacts with iron. These two reactions are exactly the reverse of 
each other because the products formed in either one of these re- 
actions are original materials for the other. Towit : 

Iron oxide plus hydrogen form iron plus steam ; 
Iron plus steam form iron oxide plus hydrogen; 

To express this in chemical symbols, we write: 
Fe 3 4 +4H 2 ^>3Fe+3H 2 

The upper arrow expresses the first statement, and the lower 
arrow the second. 

If iron oxide and hydrogen are put together into a closed vessel 
from which the air had been removed, and the vessel and con- 
tents are kept at some definite high temperature — say 1000° C. — 
until all possible changes have run their course, — and hence all 
parts of the mixture are "in equilibrium" with each other, — then 
the vessel will contain some of each of the four substances: iron 
oxide, hydrogen, iron, and steam. If, instead of the substances 
put in at first, iron and steam are put into the closed vessel, and 
it is kept at the same temperature until all possible changes again 
have taken place, then the .same four substances will be found 
within the vessel, and the ratio of the concentration of the steam 
to that of the hydrogen will be found to be the same as before. 

This result comes about as follows: We know from the pre 1 - 
ceding experiments that both pairs of substances have tendencies 
to react; hence both pairs of substances put into the vessel at 
1000° C. start to react. But, since the newly-formed pairs of sub- 
stances have tendencies to change in the reverse senses, they op- 
pose the reactions of the original substances in each case. At first, 
the force with which they oppose the reactions of the original sub- 
stances is, in each case, not large enough to stop the latter; but 
as the original reactions proceed, the reacting tendencies of the 
original substances become less in amount while that of the re- 
sulting substances increase in amount, and finally the oppos- 
ing forces become equal, reaction ceases, and the substances are 
"in equilibrium" with each other. 

The question now arises : what produces the change in the two- 
opposing reaction tendencies on account of which they are un- 
equal at first, and gradually become equal? 

6. Law of Mass Action Applied to Chemical Equilibrium. 

To answer this question satisfactorily, we must present the fun- 
damental law connecting changes in chemical activity with changes 
in concentration while the temperature remains constant. This 
is called the Law of Mass Action. 

In order to calculate changes in activity, the concentrations of 



58 Sghoch: Ixteoductoet Chemistey 

the changing substances must be expressed in numbers of mole- 
cules per unit volume (1 c.c. or 1 liter). Since the actual num- 
ber of molecules in any tangible portion of a substance is too 
large to be used conveniently, we use a larger unit, — the gram- 
molecule of each substance, which contains 6X(10) 23 real mole- 

The gram-molecule, of any substance is obtained by takix. 
many grams of it as the number which expresses its molecular 
weight. 

Thus for a gram molecule of hydrogen, we take 2 grams of it; 

:eam, 18 gra: 
The law of mass action may he stated as follows: the reaction 
tendency exerted by any single substance or mixture of *ei 
co-operating substances changes directly with the molecular con- 
ation of each substance talcing part in the change. 
In order to understand this law, let us use a few mathematical 
symbols merely to express the relations exactly, and apply the law 
to the first example of equilibrium we have studied, — the vapor- 
ization of w; 

Let the symbol of each substance placed in square brackets 
ignate the number of gram-molecules of it contained in 1 c.c. thus 
[BL] is to designate the number of gram-molecules of hydrogen 
per 1 c.c. present in a particular case. 

::t. let us express by something like a chemical equation, the 
on which takes place in the first example of equilibrium 
studied (see Chapter 2): H 2 liquid y^ H vapor. The ar- 
ire intended to show that the change is reversible, 
will now consider by itself the reacting tendency of the sub- 
stance on the left of the equation — i. e., of liquid water: — since 
it cannot var ncentration (at any definite and constant 

temperar a reacting tendency is constant, and we will ex- 

NexJ lei itt consider the reacting tendency of the substance on 
the right — its reaction tendency is proportional to its molecular 
concentration and the latter is written |~H 2 vapor]. 

obtain the actual value of the reaction tendency, we must 
multiply this expression by its proportionality constant. I 
ing the latter by K, we obtain the following valne for the react- 
ing tendency of the vapor: 

ZXfBL.0] vanor] 

Finally, we note that, at equilibrium, the two opposing tend- 
encies are equal; hence we hav- — 

ib=Z'X[H,0 vapor] 

or [H,0 vapor] =k/K= a fixed value, which means that, at con- 
stant temperature the concentration of the vapor has a fixed value 
— which accords with the fac— 



Chapter V 59 

Exercise: Write out the above argument applied to the second 
example of equilibrium, using "KN0 3 solid" and "KN0 3 dis- 
solved" respectively, and ignoring the solvent. 

7. The Law of Mass Action Applied to the Equilibrium Between 
Iron Oxide, Hydrogen, Iron and Steam. 

Let us now turn our attention to the example presented in this 
chapter, the equation for which is: 

Fe 3 4 +4H 2 ^t 3Fe+4H 2 0. 

Here we have to deal with the cooperative action of two substances 
in each mixture, and to apply the mass law we must multiply 
together the concentrations of all the substances taking part in 
the action, because if a quantity is proportional to several distinct 
numbers, then it is proportional to their product. 

We will consider the mixture on the left side first. Since the 
activity of the solid (iron oxide) is fixed, it has a certain value 
which we will represent by a. The hydrogen has four distinct 
molecules involved in the reaction, — hence it exerts its influence 
four times or acts as four distinct substances, and its effect is pro- 
portional to [H 2 ]X[H 2 ]X[H 2 ] or [H 2 ] 4 . The combined activ- 
ity of the solid and the hydrogen is proportional to: a X [H2] 4 ; 
hence it is equal to this value multiplied by the proportionality 
constant. The latter we shall designate by h; hence the combined 
activity is equal to &X&X[H 2 ] 4 . 

In the same way, we obtain, for the value of the reaction 
tendency of the mixture of the right side, the expression KXbX 
[H 2 vapor] 4 , K being the proportionality constant of this mix- 
ture and the fixed reactivity of the solid iron. 

At equilibrium, the two reaction tendencies are equal; hence 
we have 

kXaX[H- 2 Y=KXbX[H. 2 vapor] 4 . On simplifying, we obtain 

[H 2 ] 4 Kb 



[H 2 vapor] 4 ha 



— a fixed value 



[H,] 4 f Kb 

or = ^ = another fixed value. 

[ILO vapor] ha 

This equation shows that, at equilibrium at any particular tem- 
perature, the ratio of the concentration of the hydrogen to that of 
the steam is always a certain value. The value of this ratio was 
experimentally found to be 



60 Schoch: Introductory Chemistry 

0.69 at 900° C. 
0.T8 at 1025° C. 
0.86 at 1150° C. 

We are now prepared to answer the question asked at the end 
of Art. 5 above. 

The reacting tendency of either pair of the above reacting sub- 
tances, — i. e., iron and steam, or iron oxide and hydrogen — 
changes with the concentration of the gaseous member of this 
pair, because the reacting tendency of the pair is equal to the 
product of the concentration of the solid and the concentration 
of the gas, and since the concentration of the solid is constant, 
the value of the product changes with the concentration of the gas. 

When one of the original sets of substances in this experiment — 
say. iron and steam — start to react in the "closed vessel," there 
will be a decrease in their quantities with a consequent decrease 
in the concentration of the steam, and hence a decrease in the 
reacting tendencies of this pair of substance-. Furthermore, the 
iron oxide and hydrogen produced by the reaction will be present 
in small amounts at first, and although the iron oxide will be 
present in its usual concentration from the start, yet the hydro- 
gen will be present in very small concentration at first, and hence 
the reaction tendency of this pair of substances will be only slight. 
But, as the reaction proceeds, their amounts and hence their re- 
action tendency will increase steadily, while that of the original 
substances will decrease steadily: finally, the two become equal, 
and then all reaction ceases. 

In conclusion, we wish to show the application of the forego- 
ing to reactions in .general. Xearly all reactions that the student 
will meet are incomplete reactions just like the above. Those 
reactions which appear to be complete differ from the above illus- 
tration only in not reaching their equilibrium conditions until 
one or more of the original reacting substances are practically 
exhausted: but, in realitv. slight amounts of them (at least) al- 
ways remain to help maintain the equilibrium. 

Questions on Chapter V. 

1. With its temperature kept constant, is the chemical effect 
or tendency to reaction of a chemically reacting substance con- 
stant, or variable, and, if the latter, what is the amount of varia- 
tion proportional to? 

2. Describe briefly but definitely how Dumas and others made 
the earliest determination of the ratio by weight in which hydro- 
gen and oxygen combine to form water. 

3. The velocity of a chemical change is the amount of its 
products formed per second. A little reflection will show that in 
any reaction mixture kept at constant temperature the velocity. 



Chapter V 61 

and the force which impels the change, are proportional to each 
other (because the resistance or "friction" remains constant!); 
hence the velocity may be substituted for the reaction tendency 
or activity in the whole discussion of Art. 6. Repeat the whole 
argument of Art. 6 with this substitution. Equilibrium will then 
appear to be two opposed reactions taking place with equal rapid- 
ity: this is the kinetic theory view of equilibrium. It is imma- 
terial which view we take; — that of equilibrium being a balanc- 
ing of equal opposing forces, or its being due to opposed changes 
taking place with equal rapidity, — the relations and results ob- 
tained are the same. 



62 



Schoch: Inteoducioby Chemistey 



CHAPTER VI. 
ACIDS, BASES. ANT) SALTS. 

1. Introduction. 

Such substances as sulphuric acid, hydrochloric acid, a 
acid ( vinegar ), etc., have been designated as acids by all men for 
many years; while lime, caustic soda, iron oxide (iron rust), etc.. 
have been designated as bases by all men for many years. When 
any one acid and any one base are brought in contact they react 
in practically the same manner as any other acid with any other 
base, — in a manner which may be expressed briefly by Baying that 
an acid and a base react to form a salt and water. Since each 
non-metallic element is the essential component of at least one 
acid, and each metallic element is the essential component of at 
least one base, and since all acids react with all bases (to form 
the corresponding salt — and water), it is clear that the terms 
acid, base, and salt designate the three largest classes of com- 
pounds, and that the reaction between acids and bases is probably 
the most fundamental, general reaction with which we have to 
deal. For this reason it is taken up early in the course and the 
facts connected with its are presented at length. 

2. Various Examples of the Interaction of an Acid with a Base. 

Experiment (a . — Two students may work together.) Secure two 
clean burettes, put dilute hydrochloric acid into one and sodium hydrox- 
ide solution into the other. Fill each "nozzle"' full of the solution. Then 
fill the burettes to the "zero" mark (for reading the burette, see accom- 
panying figure > . Clamp the burettes in position for use. From the bu- 



M=^ 



Meniscus - Correct reodinj 
don^ line 2 



rette which contains sodium hydroxide, pour exactly 25 c.c. into a medium 
sized beaker, add 2 drops of methyl orange solution to it. secure a small 
stirring rod. and then, while constantly stirring the liquid in the beaker, 
add hydrochloric acid from the other* burette until one drop "has just 
turned'-' the color of the ''indicator-' from yellow to pink. Ascertain how 



Chapter VI 63 

much of the acid solution was used and record the amount. If the 
burettes need refilling, they should be refilled from the same supply from 
which they were filled at first in order that the solutions used throughout 
this experiment be of the same strength. This determination of the 
amount of one solution which is required for complete reaction with 
another is called "titration." 

Is there any heat given out during the reaction? 

Taste the "neutralized" solution; take a little of each of the original 
solutions, dilute them largely and then taste them cautiously. 

Pour the neutralized solution into a clean small porcelain dish, and 
concentrate it by evaporation over a piece of asbestos board until crystals 
are formed. If hydrochloric acid were thus evaporated, no residue would 
be obtained because this substance is a gas; and if the sodium hydroxide 
were evaporated, a whole solid of totally different appearance would be 
obtained. 

Enter in your note book any indications that the original substances 
have reacted. 

The weight relations in the reaction just presented are : 

NaOH+HCl=NaCl+H 2 0. 

To ascertain that the ratio between the reacting substances is the same 
irrespective of the total amounts taken, repeat the titration by starting 
with only 5 c.c. of the sodium hydroxide solution, and again by starting 
with 10 c.c. 

If instead of a soluble base, such as sodium hydroxide, an in- 
soluble base is treated with an acid, a "color indicator" cannot 
serve to indicate the "end-point" of the reaction because the in- 
dicator is affected only by solutions of bases or acids. Hence in 
treating an insoluble base we make use of other indications to 
recognize when all of the acid has been used up. How this may 
be done is shown in the next experiment. 

Experiment (b). — Into a medium sized beaker, put about 25 c.c. of 
dilute sulphuric acid, add about an equal volume of water, heat the mix- 
ture till it boils, and then add powdered copper oxide in small amounts 
at a time until some of it remains undissolved. Filter off the excess of 
copper oxide, evaporate the liquid to a small fraction of its original 
volume, and set it aside to cool. If it has been concentrated sufficiently, 
crystals of copper sulphate (CuS0 4 ,5H 2 0) will appear as the liquid cools. 

Since copper oxide itself is insoluble in water, and since the presence 
of the acid in water does not change the physical properties of the liquid 
and hence does not enable the water to dissolve the unchanged copper 
oxide, it follows that the latter must have been changed by the acid into 
a soluble substance: hence the fact that the powder disappears indicates 
that the acid is reacting with it. When the acid has been consumed, 
through this reaction the powder ceases to disappear. 

Proceeding in a manner similar to the procedure for copper oxide, try 
magnesium oxide with hydrochloric acid, and lead oxide with nitric aeid. 
Be careful not to add more than a very slight excess of the base, and 
evaporate these solutions to smaller bulk than the solution of copper 
sulphate because the magnesium chloride and the lead nitrate here pro- 
duced are more soluble than copper sulphate. 

3. Definition of the Terms: Acid, Base, Salt. 

Any substance is an acid (or a base) if it reacts with another 
substance universally recognized as a base (or as an acid, respec- 



64 Schoch: Introductory Chemistry 

tively), to form a salt and water in a manner similar to that 
shown in the preceding examples. 

4. The Essential Components of Acids, Bases, and Salts. 

Acids are compounds of hydrogen and an "acid radical" which 
may be either simple, as in HC1, or complex, as in HN0 3 . 

Bases are compounds of a metal (or its equivalent) and oxygen 
>or the hydroxyl radical (OH). 

Salts are compounds of a metal and of an acid radical. 

All of them are binary compounds essentially, — that is, they are 
■composed of two kinds of parts only. Thus potassium nitrate, 
KN0 3 , is essentially a compound of potassium (K) and the nitric 
acid radical (X0 3 ). It is less in conformity with its behavior 
to consider it as made up of the three separate elements which 
appear to enter into its composition. The two constituent parts 
of which acids, bases, and salts are thus directly compounded are 
called ions. The ions formed by metals and "acid" hydrogen are 
more particularly called cations or positive ions, and the ions 
formed by hydroxyl or acid radicals are called anions or negative 
ions. These names are derived from the names of the poles of an 
electrolytic cell, cathode and anode, since ions were first clearly 
recognized in connection with the phenomenon of electrolysis. The 
mutual action of acids, bases, and salts in solution consists of an 
exchange of these parts or ions during which exchanges the ions 
remain integral. 

5. The Relation Between the Numbers of Atoms and Radicals 

(Ions) Which Appear as Replacing Each Other in Compounds 
or as Combining With Each Other to Form Compounds. 

When we compare the formula? of any of the metal oxides 
above — for example, of sodium oxide, Na 2 — with the formula 
for water, H.,0, it appears to us that the sodium oxide contains 
two sodium atoms where the water contains two hydrogen atoms, — 
or in other words, each Xa has replaced an H. When we com- 
pare the formula for common salt, NaCl, with the formula for 
hydrochloric acid, HC1, it appears to us again that one Na oc- 
cupies the place of one H, or takes the place of the latter. In 
other words, it appears that one sodium atom always takes the 
place of one hydrogen atom. This is true for all compounds in 
which sodium atoms appear to have taken the place of hydrogen 
atoms. 

A comparison of the formula for water with the formula of 
the oxide of another metal — CaO — shows that one calcium atom 
takes the place of two hydrogen atoms : this apparent replacement 
of the two IPs by Ca is also shown by the formulae of all other 
compounds in which Ca appears in place of H. 



Chaptek VI 65 

Similarly we could show that every other metal atom displaces 
:a definite number of hydrogen atoms. 

Looked at from another standpoint, the formulas of the vari- 
ous compounds show another similar relation. When we compare 
the formula for hydrochloric acid, HC1, with the formula for 
water, H L ,0, we note that CI holds only one H combined with 
it, while holds two IPs combined with it. When we compare 
the sodium compounds of these elements, JNaCl and Na 2 0, we 
find again that the oxj'gen atom holds twice as many atoms com- 
bined with itself as the chlorine atom holds combined with it- 
self. In other words, the power of the oxygen atom to hold other 
atoms combined with itself is always twice as great as the power 
of the chlorine atom to hold other atoms combined to itself. 
►Similarly we could show that other atoms or radicals exhibit a 
definite combining power corresponding to the number of hydro- 
gen atoms they could combine with. 

On account of this constancy of the number of atoms or 
radicals which an element or radical appears to replace or com- 
bine with, we are able to figure out the formulae of the salts that 
will be formed from the basic oxide and the acids above. This 
requires merely the calculation of the proper number of metal 
atoms and of acid radicals which should be put together. For the 
purpose of calculating the numbers of these parts which belong 
together, chemists express the combining or the replacing power 
of atoms and radicals in terms of the number of H atoms which 
an element or radical can combine with or which it may replace: 
this number of H's which an element or radical can combine 
with or may take the place of is called its valence. Thus the 
valence of N~a is one, of Ca is two, of is two, of CI is one, etc. 

The formulae for the salts are obtained by placing together 
as many metal atoms and as many acid radicals, respectively, as 
are necessary to make the sum of the valences from all the metal 
atoms equal to the sum of the valences from all the acid radicals. 
Thus for aluminium sulphate we proceed thus: we take the least 
common multiple of the valences of Al and S0 4 , which is 2X3—6; 
then we ascertain the number of Al atoms which will give a 
total valence of 6 — that is, 2A1 — and we ascertain the number of 
S0 4 radicals required to give the same total valence of six — that 
is, 3S0 4 , and we write down the symbols side by side as shown 
here — Al 2 (S0 4 ) 3 , the two and three are written as subscripts 
l>ecause they refer only to a particular part of the symbol. 

6. Exercise on Formulae of Acids and Bases and on Reactions 
Between Them. 

To give the student facility in the use of symbols, formulae 
and equations, the following exercise and directions are 'here in- 
cluded. Each part — a, b, c, or d, — should be done thoroughly 



66 



Schoch: Introductory Chemistry 



before beginning the next. Failure to observe this precaution will 
produce confusion. 

(a) Commit to memory the formulae of the following bases 
and acids : 

Bases — 

Sodium oxide Xa.O 

Potassium oxide Iv O 

Calcium oxide CaO 

Copper oxide CuO 

Magnesium oxide MgO 

Zinc oxide Zn O 

Iron (ferric) oxide Fe.,0. 

Aluminium oxide 

Lead oxide PbO 

Acids — 

Name Formula Xame of Salt Formed 

Carbonic arid JL< Carbonate 

Sulphuric acid H_ v Sulphate 

Nitric acid HN Nitrate 

Phosphoric acid H PO, Phosphate 

Acetic acid H(< IT I Acetate 

Xote the relation between the terminations of the uam.es of 
the acids and of their salts. 

(b) Learn to recognize the valences of the metal atoms and 
of the acid radicals given in the compounds under (a). 

Figure out the formulae of the forty-five salts that may 
be formed from the nine bases and five acids above: do not at- 
tempt to write equations in this connection. 

Express by equations the reaction between all the acids 
and bases above. To do this put down first the formulae of the 
acid and base on the left-hand side of the equation and of the 
salt and water on the risrht-hand side. e. _.. 

CaO-H P0 4 = Ca (PO^-JLO 

Next, balance the equation without changing the formulae of any 
one of the substance- : that is. add coefficients only. Thus, in the 
examples above, add the coefficients which give the following equa- 
tion : 

3CaO+2H 3 P0 4 =Ca,(P0 4 ) 2 +3H 2 

In this reaction we have two substances — each of -which is 
composed' of two parts— forming two new substances simply by 
an interchange of parts. Tn sreneral. the change mav be repre- 
sented as follows: AB— CD=AD— CB. It must be observed, 
however, that in their recombination the four combine in accord- 



Chapter VI 67 

ance with their valences. Keactions of this general form are 
known as metathetical reactions. 

While thus learning to write equations, we must not come to 
the conclusion that we are learning to figure out what would take 
place. We can never figure out what takes place; that must be 
ascertained by actual measurement with the substances concerned. 
But the results of such measurements may be collected and ex- 
pressed in a brief statement, and the information with reference 
to the mutual actions of acids and bases is conveyed in the state- 
ment, — acids and bases react to form salts and water. The object 
of the foregoing exercise is to show the student how to apply the 
general statement to special examples. 

7. The Solubilities of the Common Acids, Bases, and Salts. 

Note. — Accurately speaking, there are no really insoluble sub- 
stances. The term "insoluble" is used here to designate sub- 
stances which are so slightly soluble that their solubility is not 
ordinarily appreciable. Yet, under certain conditions, the dis- 
solved portions of "insoluble" substances are noticeable. 

Acids: All common acids except two are soluble in water, and 
hence affect "color" indicators and have a sour taste. The insolu- 
ble acids are silicic acid, H 2 Si0 3 , and arsenious acid, HAs0 2 . 

Bases: All common bases are insoluble except: 

Ammonium hydr oxide, NH 4 0H 

Potassium hydroxide, KOH 

Sodium hydroxide, NaOH 

Barium hydroxide, Ba(0H) 2 

Strontium hydroxide, Sr(OH) 2 

Calcium hydroxide, Ca(OH) 2 

Calcium hydroxide is only slightly soluble. Naturally, only the 
soluble bases affect "color" indicators and the taste. 

Salts: The common salts have the following solubilities: 

All common salts of sodium, potassium, and ammonium are ex- 
tensively soluble in water. 

All silver salts are insoluble in water except silver nitrate, sil- 
ver acetate, and silver sulphate. The last two are only sparingly 
soluble. 

The nitrates and acetates of all metals are extensively soluble 
in water. Silver acetate is only moderately soluble. 

The sulphates of lead, barium, and strontium are insoluble; 
calcium sulphate, mercurous sulphate, and silver sulphate are 
slight!}' soluble; and all other sulphates are extensively soluble. 

The chlorides of silver and mercurous mercury are insoluble; 
mercuric chloride is moderately soluble; lead chloride is slightly 
soluble in cold water, but extensively soluble in hot water ; and all 
other chlorides are very soluble. 

The normal carbonates and phosphates of all metals are insolu- 



68 Schoch: Inteoductoey Chemistey 

ble, except those of sodium, potassium, and ammonium. (All 
acid phosphates and acid-carbonates are soluble.) 

These solubilities should be committed to memory. 

The alkali-metals are the elements of Group la of the Periodic 
System: — lithium (Li), sodium (Na), potassium (K), rubidium 
(Eb), and caesium (Cs). They are strikingly alike in the fol- 
lowing properties: 

They have the greatest tendency of all metals to change from 
free metal to compound, and this tendency increases with their 
atomic weights from Li to Cs; their hydroxides are all very solu- 
ble in water, they are extensively ionized (see next chapter), and 
hence they are said to be "strong bases": nearly all of their salts 
are very soluble; they are monovalent in all of their compounds. 

The alkaline-earth metals are the elements of Group 2a of the 
Periodic System: — glucinum (Gl), magnesium (Mg), calcium 
(Ca), strontium (Sr), barium (Ba), and radium (Ra). 

The hydroxide of glucinum is practically insoluble, and only 
feebly basic. The hydroxide of barium is quite soluble and a 
strong base: — the hydroxides of the intervening metals have in- 
termediate properties, in the order of their atomic weights. 

The tendency of these metals, to change to compounds is next 
in strength to the tendencies shown by the alkali metals. 

The alkaline-earth metals are all bivalent in their compounds. 

8. An Illustration of the Influence of Solubility Upon Chemical 
Reactions in Solutions. 

The solubilities of the substances is one of the largest factors 
which determine whether or not metathetical reaction will take 
place. Thus even in the reaction between a base and an acid, for 
which there is always a decided tendency, insolubility of the salt 
formed will retard the reaction and may prevent it practically 
entirely. The following experimental procedure serves to show 
this. The experiment is an excellent one to develop chemical 
notions : 

Experiment. — Put into each of three test-tubes a pinch of zinc oxide, 
and add to one just enough dilute HC1 so that when the mixture is 
stirred and warmed the zinc oxide dissolves. Treat the second portion 
of zinc oxide with HNO n , and the third with dilute H 2 S0 4 . In the same 
way try calcium oxide (or hydroxide), and lead oxide. Do you observe 
any relation between the solubilities of the salts that are, or should be, 
formed, and the rate at which reaction takes place? To ascertain this 
relation, tabulate your results in five vertical columns, headed, respec- 
tively : 

Base Used Acid Used, Salt to be Solubility Observed 

Formed of this Salt Rate of Change 

When a "slightly soluble" salt is to be formed, the tendency to 
reaction between the acid and the base is, in general, just as great 



Chapter VI 69 

as in any other example, but the first portions of the insoluble 
salt formed remain as a cover on the outside of each lump of 
oxide and hinder the access of the acid to the inner, unchanged 
portions of the lumps of oxide, and thus retard the progress of 
the reaction. 

9. The Hydration of Oxides. 

In Chapter I it was shown that the oxides of many elements 
hydrate on contact with water. It is intended to state here the 
most noteworthy facts concerning this hydration of oxides. 

The Hydration of Metal Oxides (Bases). — Nearly all metal 
oxides exist also in the hydrated form — as hydroxides — but only 
those oxides whose hydroxides are soluble in water react on con- 
tact with water to form hydroxides. None of the insoluble oxides 
hydrate themselves when in contact with water. 

Experiment (a). — The hydration of calcium oxide may serve to illus- 
trate the foregoing statements. Treat a few small lumps of fresh calcium 
oxide with a small quantity of water, stirring, or perhaps heating the 
mixture even, until the lumps crumble to a fine powder and all the water 
disappears. 

What has become of the water ? Has enough of it been vapor- 
ized to account for the loss in that way? Has the lime taken it 
up as a sponge takes up water? Make a special trial to decide 
this last point. Evidently the water has disappeared and is no 
longer to be found in its ordinary physical form. If this experi- 
ment were done with due precaution, and the quicklime and the 
water taken up were both weighed, it would be found that the 
two substances are in the proportion expressed by lCaO :1H 2 0. 
The formula for calcium hydroxide is written Ca(OH) . to indi- 
cate the ions it forms in solution. It may also be written 
CaO,H 2 0. The latter form shows the two oxides from which 
the compound is formed by simple combination. Formulas writ- 
ten in this manner are known as "dualietic" formulas. 

Experiment (b). — Hydration does not affect the behavior which 
metallic oxides exhibit towards acids. To show this, heat a small portion 
of hydrated ferric oxide in a test-tube to drive off practically all of the 
water of hydration, this substance being one of the hydroxides which 
upon heating will dissociate into water and oxide. Treat the resulting 
oxide, when cool, with hydrochloric acid. That an action takes place is 
seen from the fact that the powder, which itself is insoluble, dissolves 
under these conditions. Now treat a portion of the original ferric hy- 
droxide similarly with hydrochloric acid. No difference in behavior will 
be noticeable. 

10. The Formulae of the Basic Hydroxides and Their Relation to 

the Formulae of the Corresponding Oxides. 

The basic hydroxides have usually a composition which is ex- 
pressed by coupling as many hydroxyl (OH) radicals to the symbol 



70 Schoch: Introductory Chemistry 

of a metal as the valence of the latter amounts to; e. g., Al(OH) 3 . 
This is the maximum extent of hydration possible. By a loss of 
water, lower states of hydration are obtained; e. g., AIO(OH); 
and by complete "dehydration" the oxide is naturally obtained. 

Exercise: Write out the formulae of the hydroxides of all the 
metals in the list above committed to memory. 

Express by equations the complete dehydration of all these 
hydroxides. 

Express by equations the reaction between all these hydroxides 
and the acids given in Article 34 (a). 

11. The Hydration of the Acid Oxides. 

Just as hydroxides of metals — i. e., bases — are related through 
hydration to an oxide of a metal, so many oxy-acids are related by 
hydration to the oxide of a non-metal — an anhydride. Unlike the 
basic oxides, however, the acid oxides are not hydrated to any ex- 
tent that may be expressed by a general rule. Hence it becomes 
necessary to ]earn the amount of hydration in each case. The fol- 
lowing list collects all necessary details for a number of the com- 
mon oxy-acids, and these facts and relations should be learned by 
the student: 



Name 


Ion 
Formulae 


Formulae of 
Anhydrides 


Dualistic 
Formulae 


Sulphurous acid 


H.SO, 


SO, 


H,0,SO, 


Sulphuric acid 


h;so 4 


S0 3 


H,0,S0 3 


Nitrous acid 


HXO., 


N,0, 


H 2 6.X,0. 


Xitric acid 


HNO, 


X 5 0. 


H 2 0,XO, 


Phosphorous acid 


H 3 PO, 


?A 


3H.,0,P,0. 


Phosphoric acid 


H,P0 4 


PA 


3H„0,i\0 5 


Carbonic acid 


H,C0 3 


CO., 


BLO.CO, 



Note. — Salts derived from sulphurous acid are called sulphites; 
from nitrous acid, nitrites. 

Nearly all the common acids are soluble in water, and hence 
their anhydrides hydrate on contact with water. 

Experiment. — To demonstrate the hydration of acid oxides, drop a 
little phosphorus pentoxide into water. 

12. Acid Salts. 

Salts in which all the replaceable IPs of the acid have been 
exchanged for metal "atoms" are railed normal salts. It is pos- 
sible, however, to exchange only a part of the IPs in acids having 
more than one H in the molecule; since such salts still contain 
replaceable IPs, and on this account exhibit acid properties, they 
are called acid-salts. 

The formation of acid-salts takes place in the following man- 
ner: When an acid such as phosphoric, H 3 P0 4 . separates into 



Chapter VI 71 

its main constituent parts (ions), at first only one H separates, 
leaving the remainder intact as a monovalent ion (H 2 P0 4 )~; and 
when the first portions of a base are added to a solution of such 
an acid, the reaction of neutralization takes place as though ELP0 4 
were a monovalent acid, the composition of the acid radical of 
which is (H.,P0 4 )~. Hence the aluminium salt would have the 
formula A1(H 2 P0 4 ) 3 . 

Note. — The valences of positive ions are designated with plus signs — 
e. g., H + , Ca + % Al + + + ; those of negative ions with minus signs — e. g., 
€1-, S0 4 --, PO"-. 

After enough base has been added to neutralize all of the first 
set of H-ions, then the second H ionizes extensively and leaves the 
bivalent ion (HPO.J-". 

Hence when the amount of the base added to the acid is double 
that needed to neutralize the first H's in all the molecules of the 
acid, then the acid reacts as though it were composed of two 
replaceable H's and the bivalent ion (HP0 4 )~~. For example, 
the aluminium salt produced under such conditions would have 
the formula A1 2 (HP0 4 ) 8 . 

After the second hydrogen atom has been neutralized, then the 
tendency to ionize the third hydrogen atom may become effective : 
the acid then reacts as though it were composed of three H ? s and 
the ion (P0 4 ) , and forms normal salts. 

Of course if enough base is added all at once to neutralize more 
than one or two H's the reaction immediately proceeds to the cor- 
responding extent. Thus if a drop of sulphuric acid is added to 
more than enough of sodium hydroxide solution to neutralize the 
acid completely, then the salt Na 2 S0 4 is formed immediately; but 
when the procedure is reversed; that is, when a drop of sodium 
hydroxide solution is added to a great deal of sulphuric acid, then 
it will form only the acid salt (Na(HS0 4 ). 

The (experimental) formation of acid salts, with polybasic acids, 
depends only on the relative proportions of acid and base mixed. 

13. The Actual Preparation of an Acid Salt in the Laboratory. 

Secure a fresh solution of tartric acid, H 2 (CJI 4 6 ), containing about 
150 grams per liter, and a solution of potassium hydroxide containing 
about 200 grams to the liter and fill two burettes with these solutions, 
respectively. Measure out 10 c.e. of potassium hydroxide solution into 
a small flask, add 15 c.c. of the tartaric acid solution measured from 
the other burette, then heat the mixture to the boiling point, add a drop 
or two of phenolphthalein solution and finish neutralizing it by adding 
more tartaric acid from its burette. Cool the mixture under a jet of 
tap-water and add to it as much tartaric acid again as was necesary to 
neutralize the potassium hydroxide. Crystals of potassium acid-tartrate 
will be formed, according to the equation — 

K a ( C ,H 4 O e ) +H, ( C 4 H 4 4 ) =2KH ( C 4 H 4 6 ) 

Next heat the mixture to boiling and add KOH slowly, with constant 
stirring until an amount approximately equal to the original has been 



- eboch: Ixteoductort Chemistby 

added. Xote that the c— I led. Explain what 

happens in each step and write the eqn the three reactions. Note 

that the second portion :m hydroxide used is equal to the first 

m used. The com: "hat separated from the 

solut. ad they are called potassium acid-tartrate, 

or potassium bitartrate. Give reasons for both names. 

Exercise on Cnapter VX. 

1. Figure out the formulae ft - tea or bisul- 
phat- — ' aluminium. 

- ite whether or n ~ Ae to obtain 

~ ~ - id. acetic 

. - - - tee from each 

other. we _ 1 by re- 

placing one B ^placing two H'- ; 

and as tertiary those formed If 

Write out the formn' the thi ;alcium. 

4. Wi I I _-:ve equal 

-"hate, m 
ehlor . fer- 

'uminium chloride, ferric phoe igneshnn 

<ulp; 

- - the hydration wing 

faired to hydrate 
leium ox - "nhur 

I 
6. E _ q of th in the I 

im bicar 

- : the follow- 

ing substanc - 
Sulphur: 

ad. 
Phosphc : 
9 :ium hydros: 

mimum hvdroxide. 



Chapter VII 73 



CHAPTER VII. 



IONIZATION AND THE GENERAL RELATION BETWEEN DIS- 
SOLVED ACIDS, BASES, AND SALTS WHICH RESULTS 
IN METATHETICAL REACTION. 

1. Electrical Conductivity. 

If a conducting wire in an electric circuit is cut and the wire 
ends thus produced are immersed into an aqueous solution of any 
acid, base, or salt, the electric current will flow again through the 
circuit, — which shows that such solutions are conductors of elec- 
tricity. The first experiment given below is intended to show 
that the conductivity of these solutions is due to electrically 
charged particles formed from the dissolved acids, bases or salts, 

The circuit to be used in the following experiment is that pass- 
ing through a small 110-volt electric light globe. In the absence 
of an electric light circuit, a suitable magneto electric generator 
should be secured (see footnote). Cut one of the two wires lead- 
ing to the electric light. To the two open ends thus obtained 
attach covered copper wires (annunciator wire) of such length 
that they will extend into a beaker on the desk where the work 
is to be conducted. Eemove the insulation for a length of two 
to three centimeters from the ends of these wires. Secure a 
piece of ordinary glass tubing about fifteen centimeters long, and 
slip one of these wires through it until the bared end extends 
beyond the glass tube; fasten the wire in the tube by driving a 
soft wooden taper as a wedge into the tube. Then place the bare 
end of the second wire parallel beside the one fastened in the glass 
tube, and fasten the second wire securely along the outside of the 
glass tube by wrapping some "insulating tape" around the two. 
With the bare ends adjusted parallel to each other and from three 
to five millimeters apart, this "apparatus" is ready for use. When 
not in use, the annunciator wires are to be disconnected from the 
"cut" ends of the electric light cord, and the latter connected 
with screw connectors to leave them ready for future use. Al- 
though the handling of these exposed wire ends is not dangerous, 
to most people, yet it is advisable not to touch the bare wire ends 
with the fingers when the current is turned on. Care should also 
be taken to prevent their coming in contact with gas pipes, water 
pipes, or other direct connections with the ground. 

(Note. — The special magneto generator made by the Central Scientific 
Co., Catalogue, 1914, No. 2276 (price $5.00), has been found suitable to 
be used in place of an electric light circuit for this work.) 

When these ends are put into contact with different substances 
the lamp will light up with a brightness somewhat proportional 






Scsgch: T 1 1 ifi'Mwn mini ffMff ^ m ri* 



■ 

wm-GOMtu---..?~ . the lamp* will tl>:- 

- 

- 

r 

■ . ■ 






cons< lera tion oi a I&nzs 




- - ■ - • — - 

- ion. 

- 

zi ".'-•"?' ie "ionizt 

• ' " ■-■■;: ■ - ■ 



: 7T : - 



Chapter VII 75 

electric charge, and the presence of this electron on the CI is what 
is called a negative electric charge. Every ion has on it as many 
electric charges as its valence number amounts to, — thus Cu has 
two positive" charges, S0 4 has two negative charges, etc. The 
presence of these charges is expressed by various means — in this 
book a positive charge is denoted by a plus mark placed at the 
upper right-hand corner of the symbol, and the negative charge 
by a minus sign placed as usual ; e. g. : Cu + + , CI - , K + , S0 4 " ~, 
Al + + + or AF + , P0 4 - -, or TO/-, etc. 

The composition of the ions was ascertained mainly by noting 
what parts of all acids, bases, and salts appear as displacing each 
other in forming new compounds. Thus it was observed that 
hydrogen is displaced by metals, OH is displaced by the various 
acid radicals, etc., and in the absence of any indications to the 
contrary it was concluded that these interchangeable parts are the 
distinct ions. 

Not all of an acid, base, or salt in a solution is present in the 
form of ions : a part is present in the undissociated or combined 
part. This is due to the fact that the ions recombine when they 
meet. Thus it appears that there are two opposing actions pos- 
sible in solutions of acids, bases, and salts, — ionization and recom- 
bination. These two opposing actions — or rather their tendencies 
to action — hold each other in equilibrium when a certain fraction 
of the dissolved substance is in the form of ions and the remainder 
in the undissociated form. In solutions of ordinary concentra- 
tions, the various acids, bases, and salts are ionized to greatly 
different extents; but all of them increase their ion-fraction on 
dilution, and hence, in extremely dilute solution, they are all 
entirely ionized. 

3. Demonstration of the Increase of the Ion-Fraction with Dilu- 
tion and the Determination of the Value of the Ion-Fraction 
of a Certain Solution. 

Experiment. — (a) The Conductivity Trough. — Have a carpenter make 
a wooden vessel of the shape and dimensions given in the accompanying 
figure. Stout cypress or soft pine boards, at least 1£ inches thick and 
perfectly smooth on both sides, are to be used. The vessel should be as 
nearly water tight as the carpenter can make it. It should then be 
thoroughly covered on the inside with melted paraffin to make it abso- 
lutely water tight, and in order that the boards may not take up any of 
the solutions poured into it. Now secure from a plumber or cornice maker 
a piece of. fairly stiff sheet copper, at least 16 inches square. Cut it 
from one corner diagonally across to the opposite corner into two trian- 
gular pieces. If necessary, trim the short sides of the copper sheets to 
make them fit the triangular ends of the trough; but leave the excess 
of the plates at the top to be bent over the edge — to hold the plate in 
position close to the wood. 

(b) Preparing the Apparatus. — Provide any suitable means for con- 
necting the copper sheets to the wires of an electric circuit. Shake up 
about 200 grams of crystals of copper nitrate with about 50 c.c. of water 
until a saturated solution is obtained. Dilute 50 c.c. of this solution with 






SCHOCH! IXTEODUCTOEY Chemistey 




^WWWWWA 



Rheostat 




Trough 



Chapter VII 



77 



oO c.c. of water — thus securing a half -saturated solution — and pour these 
100 c.c. of solution into the trough. Secure an ammeter of the total ca- 
pacity of about one to two amperes; secure a voltmeter with a capacity 
of ten to fifteen volts; secure a source of direct electric current with a 
voltage of about ten volts (e. g,, 6-8 dry cells) ; and secure a rheostat of 
about 30 ohms resistance and a current capacity of at least one ampere. 
Connect up the apparatus and the trough as shown in accompanying figure, 
(c) Operation. — Turn on the current and adjust it with the rheostat 
until a current of about 0.1-0.2 amps, is passing. Note accurately both 
ammeter and voltmeter readings which are then shown by the instru- 
ments. In the following operations adjust the current so as to keep the 
voltage constant (at the value which has just been noted), and record in 
parallel columns the amount of the current that flows after each dilution 
of the solution. Dilute the solution by adding measured amounts of dis- 
tilled water. 



4. Eesults. 

At the beginning, the increase in current will be relatively large 
with each addition of water; then it will become less nntil finally 
no further increase in current is obtained. The following results 
were obtained in a trial in which the current source was a bat- 
tery of 5 storage cells (10 volts ! ) and the rheostat had a total 
resistance of 31 ohms. The voltage between the poles of the 
"trough" was maintained constant at 5 volts. 







Ratio of Current 








to "Maximum" Cur- 


Current per 


oliime 


Current 


rent for Whole 


100 c.c. Solu- 


(c.c.) 


(Amps.) 


Amount of Salt. 


tion. 


100 


0.16 


0.24 


0.16 


.200 


0.31 


0.47 


0.155 


400 


0.41 


0.62 


0.102 


800 


0.49 


0.74 


0.061 


1600 


0.56 


0.85 


0.035 


3200 


0.62 


0.94 


0.019 


6400 


0.64 


0.97 


0.010 


12800 


0.65 


0.98 


0.005 


14800 


0.66 


1.00 


0.004 


16800 


0.66 


1.00 


0.003 



The figures in the third column were obtained by dividing each 
value in the second column by the last or "maximum" value in 
the second column. They show that the conductivity of the half- 
saturated solution of salt used in the experiment is only 24 per 
cent of its maximum conductivity. 

The figures in the fourth column should be carefully noted in 
contradistinction to the main result just mentioned: they are in- 
tended to show that the dilute solution is really a poorer con- 
ductor than a concentrated solution, even though a larger fraction 
of the dissolved salt is ionized in the dilute solution. This dif- 



S "- . : _ x T : > : - . 

of s&lutigms. we compare the condnetino: done by equal Yorames; 

■■--''■ ' -~ ' - -'-"--- : =■!.: ■: - " :.:. ::: :>.-- zi^r v:v:.- 
trated of two solution- 

. _t -:-..i : : 7.7 •*.:::: -' : 77 - ■ : 1 " ' ..:. 

5. Changes Armrnpanying the Passage of the Electric Carrent. 

■ "--1Z.I-" -':.:■': : : ' ~ :•: - •> '•. :".:- "-r'.-vrri : f.-n-i" "•': it me :: 

. . _-. , - 

-'7 ■•■;■: •:- y.zjii-:' : ~ ;->. :>.-: "' : "-n.im- m : :>.: :_'.. 
-.77; ;t. :>.r rlr-::? 77777 r.:-- 777 - *_ -.:>-: 'i:.;7 v.- -■ 7. - ::' 
pipes or tube?, which, together with the I 7imo r 

form a elose»: 

:e pumping action of the ceD or dynamo. 

■ ' • 

- :.- "--■■ 1 7:— J «•■ '.-. •- '.-■.: 77 . :~ 7 :r 77 : 

changing copper ions to copper metal. aeccn _ 

- - . - = 

■77 7.77 nn'7 7 7 7-- 7^m7:7 777 

- 

.-,..,.- _■__ . • ... . ._ _•. . _, „,-. .^ . : .^ -;--.----:- -- . --_ 

- : - •■ _ . . - 

777 v "-*••• :"-- '•—:■ 777 77 - r ~ -7 r :r :>.- -'.''"• '•-'- 7 
:':.- .7 ■'.; - : 
• ■ ■ ■ ' 

at the surface _ per ions are produced 

77-. 7 - ' - - - - 

-*-.t 77777 :-: -- -J :e» 7 77 7- 7 77 7 7. " ■ 7 I'.-r "7.' •".- 

777 .:n? 77777 ---.--? 77- ••-77777:7-: :• 77 :: 77- i.:t: t.. 7" 
7.77- -7: :•- 77- -' -. ■- :■: -' 777777 777777 in 777 rire 

777 :i ■ - - 7 - --- - Y i-~ '..f«" -.-—--- '7s:7.r T . _ 7777- 

tons (and repel ions with the sarr 

. ■ - - 

etc. - -' -; ------ 

• 7- : — - 77. — ." -:•-- .7: :>.t 77777 -7' 7" 

the anion- Taeiee! and will -rard the anode. 

these ions arr: ' : " 

777 mi \V.:~ 777r 7777^ ' 77 ~ 77777777 "7 ~77 77 the 



- " - - — -7r ::- — ---: ■- 7--.*r- " " -- : - '.-.. -77- -^ 



Chapter VII 79 

cathode, and from the anode, respectively. Then more pole reac- 
tions will take place, and the same attendant operations will oc- 
cur: this shows that the flowing of the electric current through 
the wire depends upon the rate at which the attracted ions arrive 
at the poles. 

6. Cause of Increased Current Obtained on Diluting Solutions. 

Having learned what is taking place in the solution while' the 
current passes, Ave shall ascertain next why the current increases 
as the solution is diluted. Evidently the cause is something which 
increases the rate at which the ions arrive at the poles; hence we 
shall consider all the causes that can produce this effect. 

(1) Force attracting (or repelling) the ions: — this is kept 
constant in our experiment by keeping the voltage between the 
poles constant. 

(2) Mobility or friction that each kind of ion experiences as 
it glides through the solution : this is not changed by diluting the 
solution — as far as we know. 

(3) Distance that the ions have to travel: — it is evident that 
each ion, when attracted to the pole, will take the shortest path 
to the pole, — i. e., they w r ill travel from their original positions 
in lines perpendicular to the poles. But their "original" posi- 
tions after each dilution are at the same perpendicular distance 
from the poles as before diluting, because the shape of the vessel 
allows the dissolved material to spread out only parallel to the 
poles. To make this clearer, let us assume that the solution is 
"cut into equal thin slices" parallel to the poles — both before and 
after dilution: the slices of diluted solution will be larger than 
those of the undiluted solution, yet each one will contain just as 
many ions as the other. Thus, we see that, on the whole, the 
ions remain throughout the experiment at the same perpendicu- 
lar distances from the poles, and always have the same distances to 
travel. 

Besides the force attracting the ions, the mobilities, and the 
distances they have to travel — all of which are maintained con- 
stant and hence do not bring about the increase of the electric 
current observed, — besides these there is only one other way to 
obtain this increase, and that is by an increase in the total num- 
ber of free ions. This is the cause of the increase in current. 

In order to account for the fact that a fixed amount of a salt 
can produce different amounts of ions according to the volume in 
which it is dissolved, a Swedish chemist, Swante Arrhenius, sug- 
gested the idea that the maximum conductivity shown by a fixed 
amount of a salt in very large volum.es is due to all of it being in 
the form of ions, and the lesser conductivities it shows when con- 
fined in smaller volumes are due to the fact that only proportion- 
ate fractions of the fixed amount of salt are in the form of ions — 



Schocs: Is 

me at all 

the third a lunin of the table 

I amoun> - -*irich. are 

Bm Wn Stiamal Amounts Ionized in Common Solutions of Acids. 

Bases, and £: 

"Experiment. — Ascertain the conductivities of the following: Dilute 
:d: dilute acetic acid; dilute sodium hydroxide solution; 
ammonia solution ; sodiui: m chloride 

on ; ammonium acetate solution. 

- rials fL Is and bases dif a s 

?.l amounts ionized, while salts show no noti: 
differ * " ^re derived from acids and 

b differ _ in their fractional amour-- .vhich 

- point at- 

the fractional amounts 
■ases. and ■ ould 

• 

. and sulph 
I in aqi: 
phor • - -ulphide ) are 

:rnmonic 
nisrhly ionized. A ~nmonia) are slightly ionized. 

jhly ionized nate. 

-hloride HetCL. mer- 
curic cyanide \ nd the halides of cadmium are excep- 
tor. - 

• -tal ion and into the 

acid . wdy into Xa" and (HC 

Water :onized into H~ and OH" 

An id- ' - - 

■-ment that in a ton of water there are only 0. 

It shotild be noted 

that Insolubk r ; produce or maintain 
only few ion? in solution. 

In the table below are iriven the value? of the fractions ionized 

of some typical acids fcs, tos flier with values of the 

ionization of some acid radical 7 • - : ^resented for ref- 
erence onlv. 



Chapter VII 81 

Table of Ionization Values of Acids, Bases, and Salts in 
0.1 1ST Solutions at 18° C. 

ACIDS 

Hydrochloric Acid— HC1=H + +C1- 92.00 

Nitric Acid— HXO,— H++NO,- 92.00 

Sulphuric Acid— H 2 S0 4 =H + +HS0 4 - 47.00 

Acid Sulphate ion— HS0 4 =H + +S0 4 - - (37. per cent of 47) 17.39 

Phosphoric Acid— H 3 P0 4 — H + +H,P0 4 - 27.00 

Dihydrogen Phosphate ion — H,P0 4 =:H + +HP0 4 - - 0.14 

Monohydrogen Phosphate ion — HP0 4 =H + +P0 4 0.0002 

Acetic Acid — HAc=H + +Ac- 1.30 

Carbonic Acid— H..CO s =H + -f-HCO,- 0.17 

Acid Carbonate ion— HCO a -=H + +CO~- - 0.01 

Hydrogen Sulfide— H,S=H + -f-HS- 0.07 



Potassium Hydroxide — KOH=K + +OH~ 91.00 

Sodium Hydroxide — XaOH=Na + -f OH- 91.00 

Barium Hydroxide — Ba (OH) 2=Ba- + -f20H- 77.00 

*Barium Hydroxide— Ba (OH) o=Ba + ++20H- 92.00 

*StrontiunT Hydroxide— Sr ( OH ) ^=Sr + + +20H- 93.00 

*Calcium Hydroxide— Ca ( OH) 2 =Ca + + +20H- 90.00 

Ammonium Hydroxide — NH 4 OH==N"H 4 + +OH- 1.30 

*These concentrations are 1/64 normal. 

SALTS 

Potassium Chloride— KC1=K + +Cr- 86.00 

Silver Nitrate— AgN0 o — Ag + N0 3 - 86.00 

Sodium Acetate — NaAc=^Na + +Ac- 79.00 

Barium Chloride— BaCL=Ba + + +2CP 77.00 

Potassium Sulphate— K,S0 4 =2K*+S0 + - - 72.00 

Sodium Bicarbonate— NaHCO L< =N"a + +HCOr 78.00 

Sodium Phosphate— Na 2 HP0 4 =2Na + +HP0 4 - - 73.00 

Cadmium Iodide— CdI 2 =Cd + + +2I- 10.00 

Mercuric Chloride— HgCL=Hg + ++2C1- 0.006 

The chemical activity of acids, bases, and salts is not propor- 
tional to their total concentration, but is proportional to the con- 
centration of free ions. This general fact is strikingly illustrated 
by the great difference in the rate of action, upon zinc, of the 
strong acids (hydrochloric, dilute sulphuric) as compared with the 
slow rate of action of weak acids (acetic, phosphoric). Test-tube 
trials of these actions should be made if the facts cannot be re- 
called readily from Chapter III by the student. Compare rates of 
reaction with ionization values from the above table. 

8. Details of the Relations Between Dissolved Substances Which 
Undergo Metathetical Reactions. 

Extensive study of the reactions between acids, bases, and salts 
has led to the following conclusions : 

1. Anions and cations combine readily to form neutral mole- 



82 Schoch: Introductory Chemistry 

cules and in any solution every possible combination of the anions 
with the cations present is formed. 

2. The amount of any one combination formed depends upon 
the nature of this combination. If it has a great tendency to 
ionize, then it exerts a great force in opposition to the union of 
the ions, and the amount formed from its ions will be small, even 
if, to begin with, the solution contains many free ions of this 
combination: if the combination to be formed has a slight tend- 
ency to ionize, the extent to which the ions will combine will be 
great. 

To illustrate the above: When a solution of an acid (HC1) 
has a solution of a base (NaOH) added to it, then the two cations 
(H + and Na + ) will, on meeting the anions (CI - and OH~), form 
the four combinations,— HC1, NaCl, NaOH, HOH. Of the first 
three compounds only small amounts can be formed because their 
tendencies to ionize are so great that small concentrations of these 
substances are enough to stop further combining. But the fourth 
substance has such a slight tendency to ionize that it does not 
prevent the uniting of its ions until the supply of either H + or 
OH~ ions is practically exhausted. 

It appears from the above that the only extensive change in 
this solution is the disappearance of the H + and OH" ions which 
form water according to the equation: IP-f-OH-^ILO. 

The ordinary equation for the reaction between an acid and a 
base does not express this fart — that the reaction consists of the 
extensive combining of a pair of free ions; but it may be made to 
do this by the following modification : — express as free ions those 
substances present in greater part as free ions, and express by 
the ordinary formulae those compounds which are present in 
greater part as undissociated substances. The equation for the 
reaction betwen sodium hydroxide and hydrochloric acid will thus 
be written : 

Xa + -fOH-+H + -4-Cr=Xa + +Cr+H 2 0. 

9. Demonstration of the Disappearance of Ions in the Reaction 
Between an Acid and a Base. 

Secure three medium-sized beakers (300-400 c.c. ), fill two with pure 
distilled Avater, add to one just enough dilute hydrochloric acid (a drop 
or two) to make it enough of an electrical conductor to allow the lamp 
in the conductivity apparatus to burn dimly; then add just enough 
sodium hydroxide solution to the other beaker of water to secure a solu- 
tion of the same conductivity. Mix equal volumes of these solutions in 
the third beaker, and compare, by trial, the conductivity of the mixture 
with that of its separate components: the mixture will be found to have 
a much small conductivity. 

If ions had not disappeared, the mixture would have shown the 
same conductivity as the solutions from which it was prepared. 
The lesser conductivity indicates a decrease in the number of ions 
and thus accords with the explanation of the reaction given above. 



Chapter VII 83 

10. The Fundamental Relation Which Brings About Metathetical 
Reaction. 

According to the Mass Law (see Chapter Y, Art. 6), the com- 
bining tendency of H + with OH" ions to form H 2 is proportional 
to the expression: 

[H*]X[OH-] 

and it is equal to A*X[H + ]X[OH _ ], k being the proportionality 
constant (or, in other words, Jc is the value of the combining 
tendency when the contents of the braces have the value one). 

The dissolving tendency of water is naturally a constant because 
it cannot vary its concentration. Let this constant value be de- 
noted by K. Then, at equilibrium, we have 

,l'X[H + ]X[OH-]=Z or rH + ]X[OH-]=Z/Z;=a fixed value. 

With H + and 0H~ expressing numbers of gram-molecules per 
liter, the fixed value has been found to be 1/(10) 14 , and is 
known as the electrolytic dissociation constant for water. 

If we mix a solution of sodium hydroxide with dilute hydro- 
chloric acid, the value of the ion-product at the moment of mix- 
ing is naturally very much greater than this equilibrium value, 
]/10 34 , and their combining tendency is proportionally greater. 
But the ionizing tendency of water is still the same, and only 
great enough to produce an ion product equal to (1/10) 14 . Hence 
the combining tendency of the ions is much greater than the 
opposing ionizing tendency of the water, and therefore the ions 
combine. 

To express this relation in symbols, we write: — 

[H+]X[OH-] [H + ]X[OH-] 

in original > from pure 

mixture water 

This means that the product of the concentrations of the H + and 
OH~ ions as found in the original mixture just before reaction is 
greater than the product of the concentrations of these ions as 
found in pure water. By multiplying -these ion- products with 
their proportionality constant Jc, we obtain the relation of the 
actual values of the two opposing reaction tendencies — 

&X [H + ] X [OH-] TcX [H + ] X [OH-] 

in original > from pure 

mixture water 

But the constant may be eliminated by dividing both sides by Jc; 
hence the expression above without the constant expresses the re- 
lations of the two opposing reaction tendencies just as well. 

Naturally, reaction can take place only when the forward act- 
ing tendency is greater than the opposing tendency; and to ascer- 



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Chapter VII 85 

the quantity of the colored combination is relatively small, its 
formation used up a negligibly small quantity of ferric and sul- 
phocyanate ions, and the quantities of ferric chloride and potas- 
sium sulphocyanate put into each beaker are proportional to the 
numbers of free ferric and free sulphocyanate ions present therein 
at equilibrium. Hence the products of the numbers of cubic cen- 
timeters of ferric chloride and potassium sulphocyanate put into 
all three beakers should be the same. 

To test this, multiply the total number of cubic centimeters of 
ferric chloride by the number of cubic centimeters of potassium 
sulphocyanate used in each beaker; the product should be the 
same for all three beakers. 

12. Other Illustrations of the Fundamental Relation in Metatheti- 
cal Reactions. 

The following examples are intended to show that the many 
reactions which occur between (a) two salts, (b) between a salt 
and an acid, or (c) between a salt and a base, — which consist 
merely of the forming of new ion combinations — that all of these 
so-called metathetical reactions take place on account of the same 
general relation between the original and the resulting substances 
which was shown to exist between the acid, the base, the salt and 
water in Art. 10. It should be noted that two substances do not 
necessarily react because they are mixed : they react only when 
the substances have the relations pointed out in Art. 10. The illus- 
trations below include examples of each of the three possible com- 
binations (a), (b), and (c) above, and they also include examples 
of non-reacting mixtures. 

Experiment. — (a) Put a small lump of marble into a test-tube and 
add to it some hydrochloric acid which has been diluted to such an ex- 
tent that only a moderately rapid effervescence occurs. Then add a pinch 
or two of crystals of sodium acetate; the marble serves only as an indi- 
cator and it shows that the hydrochloric acid is not present after the 
sodium acetate is added. Of course the experiment does not show what 
change has taken place, but it disposes the student favorably to receive 
the information that a metathetical reaction has taken place. We shall 
now consider what conditions bring about this reaction. 

If a solution of sodium acetate is mixed with a solution of 
hydrochloric acid, the accidental meetings of the ions would form 
the two new combinations acetic acid and sodium chloride. 

What is the extent of ionization of each of the four combina- 
tions in the mixture? Hence do the contents of the mixture at 
the moment of its preparation show the relation which is neces- 
sary to cause metathetical reaction ? In other words, is either one 
of the following relations true? 

1. [tfa + ]X[Cl-] [¥a + ]X[Cl-] 

in original > from its own 
mixture solution 



86 - hoch: IxiEODucrosY Chemistry 

2. [H*]X[CAOr] [H + ]x[cja,o 2 ] 

in original > from its own 

mixture solution 

Evidently one of them is true, hence the reaction takes place. 
The free hydrogen and aeetions combine mostly to undissociated 
acetic acid molecules. 

This lessening of the ions in the mixture mar be demonstrated by means 
of conductivity experiments. For this purpose, dilute some hydrochloric 
acid until its conductivity is so slight that it allows the lamp to burn but 
dimly. Dilute a solution of sodium acetate to the same extent. Mix 
equal volumes of these solutions and try the conductivity of the mi . 

The equation for this metathetical reaction is: — 

H--C:-- x N -« "1-— H(C. 

Since the only change that takes place in this mixture is the 
bination of the hydrogen ions and the aeetions to form diss - 
dated acetic acid, the change is completely represented by the 
equation : 

H-- (C 2 H S 0»)-=H(C 1 H <>. . 

Experiment. — 1 1) | Repeat the above test-tube trial with sodium 
nitrate in place of sodium acetate. Docs this trial furnish any indication 
that a reaction has taken place? Consider the substances in this mixture 
a the substances of the preceding mixture were considered in the 
preceding article, and try to reason out whether or not these two sub- 
stances react. 

Although a solution of any salt mixed with the solution of any 
other salt, I or base would produce at least small amou: 
two new compound _ " NX) "=K"C1~— Xa~X 

yet such s] fciona of new compounds are not ordinarily 

t able and hence are not considered to be re o& Only the 
extensive formation of a combination of i - - oken of 3 
reaction. 

Experiment. — | c l Put a few c.c. of a concentrated solution of ammo- 
nium chloride into a test tube; note that it is practically free from any 
odor. Add some sodium hydroxide solution and note the strong odor of 
ammonia now emanating from the liquid. A metathetical reaction has 
taken place in the mixture. The formula for ammonium chloride is 
XELC1: in this substance the radical XHr is a positive, monovalent ion 
like Na* and its combination with the OH- radical is called ammonium 
hydroxide or ammonia — formula NTLOH. With this information write 
the equation for the reaction in the mixture just made. 

Proceed to make conductivity trials as in Art. 9. using a weak 
tion of ammonium chloride, a weak solution of sodium hydroxide, and 
then the mixture of these two. Finally give an explanation of why* 
the reaction takes place — following Art. 12. Experimer is a modeL 

Experiment. — d Mix in a test-tube 1 c.c. of dilute silver nitrate 
solution with a few drops of dilute hydrochloric acid: — the white solid 
which is formed is the insoluble compound silver chloride. AgCl. which 
is formed bv metathetical reaction. In this case we have visible evidence 



Chapter VII 87 

that a reaction takes place. Write the ordinary equation for it, and 
also the equation which includes only the substances that actually 
change. Consider the relations of the substances and point out why 
reaction takes place. Then, by means of your knowledge of the solubili- 
ties and ionization relations of the substances in the following mixtures, 
predict whether or not their solutions will react when mixed: — 

AgN0 3 -f-NaCl 
AgNO,+CaCl, 

Ag,S0 4 +HCl 
AgsSO.-f-NaCl 

Mix small amounts of solutions of each pair of substances and thus 
test your prediction. 

Dilute a solution of silver nitrate until its conductivity is so small 
that the lamp will glow dimly. Secure two or more of the following 
chlorides and prepare similarly dilute solutions of them: — sodium chlo- 
ride, potassium chloride, ammonium chloride, calcium chloride, magne- 
sium chloride. Then mix equal volumes of a chloride and of silver 
nitrate solutions, and ascertain the conductivity of the mixture. The 
latter will be found to be perceptibly less than that of either constituent. 
State why. 

Experiment. — (e) Mix in a test-tube one c.c. of a barium chloride 
solution with a few drops of dilute sulphuric acid: the white solid which 
appears is the insoluble compound, barium sulphate, BaS0 4 , which is 
formed by metathetical reaction. In this case we have again visible evi- 
dence that a reaction takes place. Write the equation. Consider the 
relations of the substances and point out why reaction should take place. 
Then predict, from your knowledge of the solubilities and ionization re- 
lations of the substances in the following mixtures, whether or not their 
solutions react; — 

BaCL+NaoSO, 

BaCL+MgSO, 

Ba(N0 3 ) 2 +H 3 S0 4 

Ba(N0 3 ) 2 +MgS0 4 . 

Mix small amounts of solutions of these substances in test-tubes and 
thus test your predictions. 

Make the usual conductivity trials with a dilute solution of barium 
chloride, with a dilute solution of a sulphate, and with a mixture of the 
two. State why the mixture should have a lesser conductivity than its 
separate components. 

13. An Example of a Metathetical Reaction Brought About by 
Precipitating" One Compound by Concentrating the Solution 
(and Another by Cooling-). 

Weigh out, on a platform scale "to the nearest gram," 25 grams of 
commercial sodium nitrate (Chile saltpeter) and 22 grams of commercial 
potassium chloride. Measure out 50 c.c. of distilled water, and heat 
this to boiling in a porcelain dish. While continuing to heat the dish 
with a medium-sized flame, add the sodium nitrate and stir the liquid 
with a glass rod until the crystals are dissolved. Then add the potas- 
sium chloride, and stir the mixture until this salt has dissolved. In- 
crease the flame, and while steadily stirring the mixture, evaporate it 
rapidly to one half the bulk. Then allow the crystals to settle, decant 
the liquid as completely as possible into a small beaker, holding back 
the crystals, and finally press them with a spatula to get all the liquid 
possible out of them. They are crystals of common salt — sodium chloride. 



3 hoch: Introductory Chemistry 

Allow the liquid to cool thoroughlv: the ervstals which appear are 
composed of potassium nitrate. If neeessarv. the cooling of the liquid 
mar be hastened by putting the solution into a small flask, and coolino- 
its bulb with tap-water. However, the crystals obtained will be smalf. 
Finally, decant the liquid, dry the cr een a ft f fil- 

ter paper, and give them to the instructor in order -hi- fairlv 

valuable salt. 

Look up the solubilities, at 100' C. and at 2 etivelv. of the 

four salts involved in this reaction: which salt will be precipitated first 

solution is concentrated? Note the relative amount of this same 

salt which will be precipitated on cooling the solution. Which salt will 

be precipitated extensively on cooling. Why? 

Questions on Chapter VII. 

1- State etical reaction will take place 

when solutions of the following pairs of re mixed, 

and point ont which ion pair fulfills the fundamental condition 
that brings about the reaction. Then prepare in test-tubes small 
amounts of these mixtures. Do the res als agree 

with your predict: 

^•diurn carbonate and sulphuric acid. 
e phite and hydrochloric a 
9 diuni carbonate and calcium chloride. 
S iium chloride and acetic acid. 
Sodium chloride and copper sulphate, 
^•dium phosphate and copper nitzmJ 
9 iium hydroxide and copper sulphate. 

sidered in the light of the ion theory, what takes place 
in every metathetical reaction which may be looked upon as the 
real reaction taking place ? Illustrate with three distinct examples 
from your own experience in this cour- 

3. State the extents of ionization of the common ac: 
and salts. 

4. Given the apparatus for the experiment in . properly 
connected for the beginning of the experimer' — si be what is 
done in performi: _ i <eriment^ and show how the larger cur- 
rent obtained in diluting the solution must be due to the fact that 
the fraction salt which is ionized increases with dil 
Show that all other possibilities for the incr - ire prevented by 
the conditions of the experiment. 

5. If only 1 per cent of the acetic acid in a solution is in the 
form of : nee only ions react, how does it happen that 
all of the acid will be neutralized when suit: jm hydroxide 
solution is added? 

6. How does the r>er cent of ionization c : ind salts 
change with dilution? Hence, does dilute hydrochloric acid con- 
tain more ions per c.c than concentrated hydrochloric acid? 
Ez: ■'. - ■•_: 



Chaptee VII 89 

7. A liter of acetic acid solution contains, at equilibrium, 1 
gram-molecule in the form of unionized molecules, and 0.0042 
gram-ions of free H + ion and of (C 2 H 3 2 ) _ ion, respectively: cal- 
culate the value of this "equilibrium" ion-product. 

If hydrochloric acid gas is absorbed by this solution until the 
solution contains 0.1 gram-ions of free H + ions, approximately 
how many free acetions are left? 

Suggestion: At equilibrium, the following relation exists: — 

fcX [H + ] X [C 2 H 3 2 -] =KX [H ( C 2 H 3 2 ] 

I- and K being the usual proportionality constants (see Chapter V, 
Art. 6). Dividing by h, we obtain 

[H + ]X[C 2 H 3 2 -]=^/^X[H(C 2 H 3 2 )] 

K and h are fixed numbers; and since the amount of unionized 
acetic acid can be increased only from 1 to 1.0042 by the forma- 
tion of more molecules through the union of the ions present, 
we may consider this number of unionized molecules constant, — 
hence all of the right side of the equation above is constant, and 
hence the left-hand side must be constant. This means that 
the ion-product must remain constant while the HC1 gas is added. 
With this simplification, the problem is easily worked. 

8. A solution of sodium acetate contains 1.1742 gram mole- 
cule per liter which we will assume to be completely ionized; a 
solution of hydrochloric acid contains 1.0001 gram molecules per 
liter — also assumed to be completely ionized. If one gram-mole- 
cule of unionized acetic acid is formed after the solutions are 
mixed, will the remaining ions (of H + and of C 2 H 3 2 ~) remain 
free? Explain by calculating. 

How much greater is the combining tendency of the H + and 
acetions in the above mixture just at the moment of mixing as 
compared with their combining tendency at equilibrium? 

9. A certain solution of copper nitrate, when first put into 
the "trough" in Art. 3, has such a conductivity as to allow 0.43 
amperes to pass. As the solution is diluted gradually, and the 
voltage is kept constant, the current increases to 0.68 amperes 
and remains at this value although the solution is diluted further. 
Calculate the fraction of the salt in the original solution which 
was in the form of free ions. 



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Chapter VIII 91 

high temperature and continue to burn. When the latter forms 
are heated without access to air to a very high temperature 
(3500° C.) they change to graphite. 

Experiment. — (a) (In all experiments in this chapter, two students 
may work together.) Place a porcelain crucible on a clay covered triangle, 
tilting it so that it rests on its side. Put a small piece of charcoal into 
the crucible and heat it with a burner to ascertain how readily it burns. 
Then try a piece of graphite in the same manner. Although these two 
substances are identical in composition, yet they are quite different in 
properties. This is generally true of allotropic forms of a substance. 

When equal weights of different forms of carbon are burned to 
carbon dioxide, they give out different amounts of heat, as ex- 
pressed in the following equations: 

C (lampblack) +0,=C0 2 (gas) +97,650 cal. 
C (graphite) +0 2 =C0 2 (gas) +94,810 cal. 

The difference between these amounts — i. e., 2,840 cal. — is the 
amount of heat given out when 1 C of lampblack (12 grams!) 
changes to 1 C of graphite. This change is similar to the change 
of liquid H 2 to solid H 2 (ice), — in which change 1.428 cal. are 
given out when 1 H.,0 (18 grams) changes. 

Solid forms of the same element which differ in properties as 
these forms of carbon differ, are called allotropic forms of the 
element. Other elements which exist in several allotropic forms 
are sulphur, phosphorus, tin, etc. 

At high temperatures, carbon combines directly with oxygen, 
hydrogen, nitrogen, sulphur and other elements. When air or 
oxygen is admitted sparingly to hot carbon, carbon monoxide — 
CO — is formed, but when this CO is mixed, hot, with more 
oxygen, or with substances which give up oxygen, then it changes 
to C0 2 . When air is admitted sufficiently rapidly to hot carbon, 
it forms C0 2 immediately. 

Many compounds of carbon and hydrogen exist, but only a few 
can be formed by direct contact of hydrogen with hot carbon. 
Combustible gases used in everyday life are composed largely of 
the compound CH^ — methane or marsh gas — or they contain 
CO — and some of them also contain hydrogen. It is such gases 
which in furnaces reduce metal oxide to free metals. 

Experiment. — (b) Secure a piece or a stick of charcoal, and boil it 
in a concentrated solution of sodium carbonate. This treatment renders 
it practically non-combustible and the stick will thus serve as a suitable 
holder for the metal oxide. 

Close the air holes of a Bunsen burner, and turn down the flame to one- 
third its usual height. Moisten the end of the charcoal stick and dip it 
into some powdered lead oxide, then hold it in the center of the flame: — 
globules of metallic lead will appear immediately. 

Hot carbon combines directly with sulphur to form carbon bi- 
sulphide — CS 2 — which is a clear liquid at ordinary temperatures. 



92 Schoch: Ixteoductoby Chemistry 

Carbon does not combine directly with nitrogen, but a com- 
pound of carbon and nitrogen can be formed in an indirect way. 
It is known as cyanogen, and has the formula (CN) 2 . It is an 
extremely poisonous gas. Compounds of cyanogen with metals or 
hydrogen are called cyanides. Of these, potassium cyanide — 
KCX — and prussic acid — HCX — are the best known. All 
cyanides are violent poisons. 

Compounds of carbon and metals — called carbides — are familiar 
to everybody through calcium carbide, CaC : . These carbides re- 
act on contact with water in a manner illustrated by the behavior 
of calcium carbide, which reacts according to this equation — 

CaC 2 +2H 2 0=Ca(OH) 2 =C 2 H 2 . 

The compound C 2 H 2 is the familiar substance called acetylene. 

3. The Properties of Carbon Dioxide. 

Carbon dioxide is formed whenever any combustible substance 
containing carbon is burned with free access of air. It is formed 
slowly during the decay of animal and vegetable matter. It oc- 
curs extensively in nature in the compound CaC0 3 , which in its 
pure, crystalline form is known as marble or cdlcite. It also 
occurs in another crystalline form known as Aragonite or Dog 
Tooth Spar. Calcium carbonate is also the main component of 
limestone, of oyster shells, and of much other earthy material. 

Carbon dioxide is a colorless, practically odorless gas. It is 
very heavy — about 1.5 times as heavy as air. It is fairly soluble 
in water : 1 volume of the gas dissolves in 1 volume of water at 
ordinary temperatures. It can be liquefied at 20° C. by compress- 
ing it under t56.3 atmospheres pressure. 

Dissolved in water, it forms carbonic acid, H 2 C0 3 , and this 
acid forms normal carbonates with all bases except the bases of 
the trivalent ions (e. g., Al + + + and Fe + + + ). When heated, the 
carbonate of bivalent metals dissociate into carbon dioxide and 
the oxide of the metal, — as shown by the equation — 

CaC0 3 =CaO+C0 2 . 

The carbonate of Ca, Sr, and Ba dissociate much less extensively 
(or require a higher temperature) ihan the carbonates of the other 
bivalent metals. The carbonates of sodium and potassium — Xa 2 
CO.-, and K 2 C0 s — are stable even at high temperatures. The 
fact that the trivalent metals — Al and Fe — do not form carbonates 
indicates that the carbonates of these trivalent metals dissociate 
completely at ordinary atmospheric temperatures. Hence, when 
all the carbonates are arranged in the order of the temperatures 
required for their dissociation into metal oxide and carbon di- 
oxide, they appear in the following order : Xa 2 C0 3 and K 2 C0 3 — 



Chapter VIII 93 

stable even at high temperatures; CaC0 3 , SrC0 3 , BaC0 3 — disso- 
ciate at red heat; ZnC0 3J CuC0 3 and other bivalent metal car- 
bonates — dissociate at temperatures below red heat; Al and Fe 
carbonate — dissociate at ordinary temperatures, — hence not formed 
at ordinary temperatures. 

Experiment. — The Preparation of Carbon Dioxide, and the Demonstra- 
tion of Some of Its Common Properties. 

Fit up a 500 c.c. flask with a two-hole rubber stopper, a dropping fun- 
nel, and a delivery tube made by bending an ordinary glass tube, six 
inches long, near its mid-point to a right angle. 

Secure another piece, twelve inches long, and bend it near one end to a 
right angle. Heat the ends of these tubes until the sharp edges have be- 
come rounded by slight fusion. Secure a two-inch piece of small — suit- 
able — rubber tubing, and connect the short arm of this glass tube to the 
right-angle tube fitted in the stopper of the generating flask, and by means 
of this "conducting" tube pass the gas into the different vessels and sub- 
stances as directed below. 

Put into the flask a handful of powdered sodium carbonate (commer- 
cial washing soda). Moisten the salt with water and when ready to 
collect the gas, allow dilute sulphuric acid to drip into the flask from the 
dropping funnel. The substances first react metathetically to form H a C0 3 , 
and then this substance dehydrates: — 

Na 2 + C0 3 - -+H/S0 4 - -=^a, + S0 4 - -+H,C0 3 
HzCO—HoO+CO;. 

(a) Pass carbon dioxide into a little distilled water in a test-tube 
until the water is saturated (to determine the latter, close the test-tube 
with the thumb, shake it vigorously, and note whether or not a partial 
vacuum is created in the tube). Does the gas appear to be very soluble? 
Try blue litmus paper on this solution? What ions must be present to 
produce this change of color? Show by an equation how they were pro- 
duced. # 

Experiment. — (b) Place a small piece of burning candle at the bot- 
tom of a large beaker and allow carbon dioxide to flow into the beaker 
until the flame is extinguished. 

(c) Pass carbon dioxide downward into a dry, wide-mouth bottle (500 
c.c.) while keeping the mouth of the bottle covered as well as possible 
with a piece of glass. Fasten some magnesium ribbon to the end of a 
piece of iron wire, ignite it, and lower it into the bottle: then try to find 
the carbon produced. Write the probable equation of this reaction. The 
burning of the magnesium in this gas is due to the high temperature 
created by the large amount of heat evolved from the reaction: this tem- 
perature is high enough to dissociate carbon dioxide into oxygen and CO, 
or into oxygen and carbon, and thus oxygen becomes available for the 
continuation of the combustion. 

(d) Put about 50 c.c. of clear lime water into a small conical flask, 
allow carbon dioxide to pass into this solution until the precipitate 
first formed is redissolved, and then boil the solution. 

4. Relation Between the Components of a Carbon Dioxide Solution. 

A glance at the equations above and at the equation called for 
in (a) reveals the fact that in experiment (a) dioxide and water 
combine, while in the preparation of carbon dioxide they separate. 
Evidently this change is reversible; as in all such actions, so in 



9-1 Schoch: Introductory Chemistry 

this, equilibrium is attained when the concentrations of the sub- 
stances on the two sides of the equations bear a certain ratio to 
each other. If the relative concentration of H 2 C0 3 is greater 
than this ratio, it breaks up into C0 2 +H 2 and if its relative 
concentration is less than this ratio, then C0 2 and H 2 combine. 

Every aqueous solution of carbon dioxide has, in addition to the 
equilibrium just pointed out, another equilibrium — namejy, be- 
tween the gas C0 2 and the dissolved C0 2 ; the gas dissolves in 
water or is liberated from the water until the concentration of 
the C0 2 gas above the water bears a certain ratio to the dis- 
solved C0 2 . 

Hence a saturated aqueous solution of carbon dioxide presents 
the following equilibria : 

(1) C0 2 (gas) 7"* CO, (dissolved) 

(2) C0 2 (dissolved) 4-H 2 0^±H 2 C0 3 (undissociated) 

(3) H 2 C0 3 (undissociated)^ H + +HC0 3 - 

(4) hco,-^:h + -lco3-- 

Thus, it is seen that there are four distinct equilibria existing 
in an aqueous solution of carbon dioxide. In connection with the 
last two equilibria, it should be recalled that all polybasic acids, 
such as H 2 CO,, IT >. II SQ 4 . and H,P0 4 , have a much smaller 
tendency to ionize the second H* ion than the first H + ion, and a 
still smaller tendency to ionize any other H + ions present (as in 
H^P0 4 , for example). In this connection, look up the ionization 
values of polybasic acids given in the table in Chapter VII, Art. 
7. It is on account of this lesser tendency to ionize that such 
acids form acid salts : with the first set of H + ions such acids act 
as stronger acids than with the second set. 

By treatment with carbon dioxide dissolved in water, all car- 
bonates are changed to bicarbonates or acid-carbonates. All bi- 
carbonates are soluble in water, — and since the carbonates of the 
bivalent metals are insoluble, it follows that their conversion to 
bicarbonates is accompanied by the dissolving of these insoluble 
carbonates. 

The bicarbonates of metals other than the alkalies are stable 
only in water charged with carbon dioxide. When the water loses 
this free, dissolved carbon dioxide, the bicarbonates change back 
to the normal salts according to the equation — 

Ca(HC0 3 ) 2 =CaC0 3 +H 2 C0 a 

"=CaC6 8 +H 2 0+C0 2 . 

Hence, when such solutions are boiled, the dissolved solids sepa- 
rate from the solution. 



Chapter VIII 95 

Since natural water may secure carbon dioxide from the air, 
from decaying vegetable matter, etc., it frequently happens that 
natural* water which has passed over limestone rocks contains 
large quantities of calcium bicarbonate, and when this water is 
boiled, calcium carbonate separates from the solution. 

This deposition of calcium carbonate is often noticed when nat- 
ural waters are boiled : the water becomes slightly opaque at first 
and afterwards clears up again when the insoluble calcium car- 
bonate has settled. The bicarbonate of calcium (and of mag- 
nesium) in waters is known as ' 'temporary hardness," due to the 
fact that it can be removed quite easily (a) by boiling or (b) by 
the addition of calcium hydroxide. The reaction of (a) is 

Ca(HC0 3 ) 2 =CaC0 8 -fC0 2 +H 2 

and the reaction produced by the addition of Ca(OH) 2 is one of 
again changing the acid salt back to the normal salt, or 

Ca(HC0 3 ) 2 +Ca(OH) 2 =:2CaC0 3 +2H 2 0. 

The bicarbonates of sodium, of potassium, and of ammonium 
do not dissociate but slightly at ordinary temperatures, and hence 
may be obtained outside of solution — as dry salts. However, their 
dissociating tendency increases markedly with the temperature, 
and they change to monocarbonates, according to the equation — 

2NaHC0 3 =Na 2 C0 3 +H 2 0+C0 2 . 

Sodium carbonate is known in commerce as sal soda, while the 
bicarbonate is known as cooking or baking soda. Sodium bicar- 
bonate is less soluble than sodium carbonate. 

5. The Fundamental Relation Which Brings About Metathetical 
Reactions in the Preparation of Carbon Dioxide. 

The fundamental relation on account of which sodium carbo- 
nate solution and dilute sulphuric acid react is evidently — 

[H-]X[C0 3 --]>[H+]X[C0 3 --] 
in original from saturated 

mixture solution of H 2 C0 r> 

The expression on the right is small for two reasons: first be- 
cause the solubility of carbonic acid is small, and, second, be- 
cause this small amount of carbonic acid is only slightly ionized. 
It is hence not surprising that all carbonates — even so-called in- 
soluble carbonates — react when mixed with any, even weak, acids. 
Hence in general it may be said that carbon dioxide may be pre- 
pared by taking any carbonate and treating it with any acid. 

Make test-tube trials with several different acids and carbo- 
nates to demonstrate the above statement. Write all equations. 



96 Schoch: Ixteoductoey Chemistey 

In practice, sulphuric acid would not be used with calcium car- 
bonate. Why ? 

6. Carbon in Its Relation to the Other Members of Its Periodic 
Group. 

Keference to the Periodic System (Chapter I, Art. 13) will 
reveal that carbon is in Group IV; associated with it are silicon 
(Si), germanium (Ge), tin (Sn), and lead (Pb). The atomic 
weights range from 12 to 207 in the order given. Of this group, 
carbon is the typical element, being essentially non-metallic and 
forming an acid oxide — C0 2 . Silicon approaches the metallic 
state more nearly, although its oxide — Si0 2 — is still acidic. The 
other metals, Ge, Sn, and Pb become more metallic in nature and 
their oxides (of the general form M0 2 ) are basic in nature. Ge0 2 
is the transition oxide, having both acidic and basic properties. 

Carbon and silicon exhibit a close relationship chemically: (a) 
they both exist in similar allotropic modifications; (b) they form 
similar hydrogen compounds, CII 4 and SiTT 4 ; (c) they form sim- 
ilar oxides, CO_, and SiO a (sand) : and (d) they both form chloro- 
form compounds, CHC1 3 and SiHCl 3 . 

It must be noted that carbon is dissimilar in certain respects 
from the other members of the group: (1) its oxides (CO and 
C0 2 ) are both gases, while the oxides of the other members are 
solids, and (2) it forms a much larger number of compounds 
with hydrogen, oxygen, nitrogen, etc., than any of the other 
members, constituting the laruv field of organic chemistry (see 
Chapters XIII and XIV). 

The fact that the member of the first short period (carbon) 
differs more from the other members of its group (Si, Ge, Sn, 
Pb) than the latter differ among themselves, — this peculiarity ap- 
pears also in all the other groups. 

7. The Properties of Sulphur. 

Sulphur is found in the earth in the form of the free element, 
and hence its preparation for commercial use consists merely of 
its separation from the earthy constituents mixed with it. It is 
also obtained commercially in heating iron pyrites — fool's gold — 
without access of air. Under these conditions, iron pyrites give 
up sulphur in the proportion by weight indicated by the equation — 

3FeS 2 =Pe s S 4 +2S. 

(Compare this equation with that for the decomposition of man- 
ganese dioxide at high temperatures ! ) . 

Experiment. — (a) Heat a little iron pyrites in a test-tube, and note 
the free sulphur formed. 

Sulphur has an indefinite but low melting point. Its boiling 



Chapter VIII 97 

point is 444.6° C. In its chemical conduct it resembles oxygen 
in so far as it unites directly with, metals, and it unites with 
hydrogen to form hydrogen sulphide, H 2 S, and with carbon to 
form CS 2 . A comparison of these two formulae with H 2 and 
CO,, respectively, shows the similarity between the chemical prop- 
erties of sulphur and oxygen. 

Experiment. — (b) Bend a test-tube slightly at the mid-point, and 
put some sulphur into it; melt this and distill it, allowing it to drop 
into some water, — merely to show that it can be melted or distilled. 

Mix intimately some very fine iron filings with an equal bulk of sul- 
phur: put the mixture into a test-tube, and start it to reacting by heat- 
ing the lower end of the tube until the glow started there proceeds prac- 
tically of its own accord up through the mass. Show that a new sub- 
stance has been formed; for this purpose add hydrochloric acid to small 
amounts of the original and of the resulting substances, and note any 
differences in the behavior of these mixtures. The iron and sulphur com- 
bined in the ratio expressed by FeS. 

The common compounds of sulphur belong to the following 
three classes: 

(1) Sulphides — related to or derived from H 2 S. 
• (2) Sulphites — related to or derived from H 2 S0 3 (or S0 2 ). 

(3) Sulphates — related to or derived from H 2 S0 4 (or S0 3 ). 

The properties of the sulphides and of hydrogen sulphide will 
be studied farther on. 

8. The Properties of Sulphur Dioxide. 

Sulphur dioxide is the only product obtained whenever sulphur 
is burned in air or oxygen. It is a colorless gas, with an irritat- 
ing odor. It is very heavy — about 2.2 times as heavy as air. It 
is very soluble in water: 1 volume of water dissolves 80 volumes 
of the gas. It is easillv liquefied because its boiling point is 
—10.1° C. 

In its chemical behavior — i. e., in the formation and dissocia- 
tion of sulphites and bisulphites, sulphur dioxide acts just as 
carbon dioxide does ; but it differs from the latter in the fact that 
it has a tendency to take up more oxygen and change to S0 3 . 
It shows this tendency even when it is dissolved in water — i. e., 
when it is in the form of H 2 S0 3 , it tends to form EUSO^. This 
tendency is the most notable property of sulphur dioxide. The 
manufacture of sulphuric acid makes use of this tendency of 
SO, to combine with oxygen. 

The bleaching action of sulphur dioxide is due to the fact that 
it forms colorless compounds with the "carbonaceous" colors. 
Since these compounds dissociate again, the bleaching effect is not 
permanent. 

Experiment. — (a) The Preparation of Sulphur Dioxide and the Dem- 
onstration of Some of Its Properties. 



98 Schoch: Ixtkoductory Chemistby 

Prepare sulphur dioxide from a "mush" of bisulphite of soda and con- 
centrated sulphuric acid, using the same apparatus as for carbon dioxide. 
As in the preparation of carbon dioxide, the substances first react meta- 
thetically to form H 2 S0 3 , and then this substance dehydrates — write the 
equations. 

(b) The Oxidation of Sulphur Dioxide by the Oxygen of the Air. 
Saturate 100 c.c. of Mater in a flask with the gas obtained in (a). Test 

the solution with litmus. Test a few drops of it by adding first a few 
drops of hydrochloric acid and then a few drops of barium chloride solu- 
tion. Since barium sulphite is soluble in water, should there be any reac- 
tion ? Put 20 c.c. of the same solution into a medium-sized flask and 
shake it vigorously so as to bring it extensively into contact with the 
oxygen of the air. Test again with hydrochloric acid and barium chlo- 
ride. Note difference from preceding trial and explain, giving all equa- 
tions. 

(c) The Oxidation of Sulphur Dioxide by Means of Oxidizers. 

Take another portion of the solution above and add to it potassium 
permanganate solution, a drop at a time, until no further change occurs. 
The color change shows that the permanganate is reduced: — that it gives 
up oxygen. Oxidize still another portion of the solution with a little 
concentrated nitric acid and note the brown fumes formed; these indi- 
cate that the nitric acid has been reduced. Test the resulting mixtures 
with barium chloride solution. 

(d) Bleaching Action of Sulphur Dioxide. 

Moisten some flowers and expose them to the sulphur dioxide in a flask: 
note that the color disappears. 

State briefly the properties of sulphur dioxide which have thus 
been shown experimentally. 

Point out the fundamental relations which brings about meta- 
thetical reaction in the preparation of sulphur dioxide by the 
method prescribed above. 

When sulphur dioxide is absorbed in water, the same changes 
take place as with carbon dioxide. Write out the equations for 
the equilibria, in this solution. 

Write in proper order the equations for the reactions that take 
place when sulphur dioxide is absorbed in an excess of sodium 
hydroxide. If sulphur dioxide is added to the mixture after the 
sodium hydroxide has been neutralized, what reaction will take 
place then ? 

9. The Common Properties of Sulphuric Acid. 

The manufacture of sulphuric acid should be demonstrated ex- 
perimentaly on the lecture table. 

Experiment. — Secure a clean, dry beaker of about 100 c.c. capacity, 
and a clean (dry!) burette with a glass stop cock. Fill this with con- 
centrated sulphuric acid. (Be careful not to get any drop of this acid 
on the skin or on the clothing, but should this happen, remove it imme- 
diately by means of a large amount of water. Clothing should finally 
also be moistened with dilute ammonia.) 
Weigh the beaker accurately and record the weight. Then pour into it 



Chapter VIII . 99 

exactly 25 c.c. of sulphuric acid from the burette, and weigh the beaker 
and contents- Subtract the weight of the empty beaker from the latter 
weight, and divide the remainder by 25 c.c: — the quotient is the specific 
gravity of the acid at room temperature. How much heavier than water 
is the acid? 

Put the beaker with a wire gauze under it on a ring-stand in position 
to be heated. Secure a thermometer with a range of 200° C. or more, 
and suspend it in such a position that its bulb will be immersed in the 
acid in the beaker. Secure a large dish or tin pan, fill it with tap-water, 
and keep it in readiness to catch the acid in case the beaker breaks. Heat 
the acid slowly with a medium-size flame until the thermometer indicates 
about 190° C. Note that the acid does not boil even at that temperature. 
It is unprofitable, and somewhat dangerous to try to heat the acid to its 
boiling point (338° C.) and the above heating suffices to indicate that 
the boiling point of the acid is very high. Do not disturb the apparatus 
until the acid has cooled to 60° or below: — then pour it back into the 
supply bottle, and wash the apparatus with a large amount of water. 

Fill the test-tube half full of distilled water, put it on the test-tube 
rack, and add to it slowly about one-eighth of a test-tube full of concen- 
trated sulphuric acid. Note the large amount of heat liberated when sul- 
phuric acid is diluted with (dissolved in!) water. 

Whenever concentrated sulphuric acid and water are to be 
mixed, the acid should be poured into the water: the acid, being 
heavier than the water, sinks through the latter and thus helps 
to mix the liquids. With the reverse procedure, the water tends 
to float on top of the acid, and the great evolution of heat under 
the water may produce an "explosive" formation of steam. 

10. Sulphur in Its Relation to the Other Members of Its Periodic 

Group. 

Sulphur is found in the sixth group of the Periodic Classifica- 
tion. Associated with it are found oxygen, selenium (Se), and 
tellurium (Te). Each of the members of this group form hydro- 
gen compounds — hydrides — of the general formula H 2 E, such as 
H 2 0, H 2 S, H 2 Se, and H 2 Te. The oxygen compound, H 2 0, as 
we know, is an odorless liquid at ordinary temperatures, while the 
others are nauseating, poisonous gases. 

Sulphur, selenium, and tellurium each combines with oxygen 
forming similar oxides — S0 8 , Se0 3 , and Te0 3 and S0 2 , Se0 2 , 
and Te0 2 . The members of this family or group pass by regular 
gradation from the gaseous, non-metal, oxygen to the almost me- 
tallic, slightly basic tellurium. Of the four elements, their abund- 
ance in nature is inversely proportional to their atomic weights: 
tellurium exists only in very small quantities, while oxygen is 
found in abundance. 

11. The Properties of Ammonia. 

Ammonia (NH 3 ) is a gas which is obtained as one of the prod- 
ucts when animal or vegetable remains are heated without access 
of air, as is done when coal is heated in gas manufacture. Am- 



100 Schoch: Introductory Chemistry 

monia is also made by the direct union of its constituent ele- 
ments, nitrogen and hydrogen. Ammonia is a colorless gas with 
a strong suffocating odor. It is about one-half as heavy as air. 
It can be liquefied by pressure, and its boiling point is — 33.5° C. 
It is very soluble in water: under a pressure of 1 atmosphere. 1 
volume of water at 0° C. dissolves 1298 volumes of ammonia, and 
1 volume of water at 20° C. dissolves '710 volumes of the gas. 

When dissolved in water, a part of the ammonia is hydrated to 
NH 4 0H. This substance ionizes into NH 4 + and OH" ions. On 
account of the similarity between the NH 4 + ion and the sodium 
or potassium ions, the NH 4 + ion is called ammonium. (ISTote the 
termination iuml) 

The hydration of ammonia is a reversible reaction and leads to 
equilibrium relations expressed schematically as : 

NH 8 (gas) ^± NH 3 (dissolved) 

NH 3 (dissolved) +H 2 7^: NH 4 OH 

xrr 4 oH^ixH 4 + +on- 

Hence there are three distinct equilibria in any aqueous solu- 
tion of ammonia ; a removal or increase in any member of any 
of the equilibria will cause a shifting of the entire equilibria 
chain in such a direction as to adapt itself to the change. (Le 
Chatelier's principle.) 

Experiment. — (a) Heat a small piece of gelatine in a dry test-tube. 
Note the odor ( ? ) . 

Experiment. — (b) Secure a snip 11 flask (200-300 c.c. capacity), a 
one-hole stopper, and a piece of ordinary narrow glass tubing about eight 
inches in length. Push the glass tube barely through the hole in the 
stopper, and put the latter in the neck of the flask so that the tube will 
extend outward. Secure an ordinary, narrow-mouth bottle (not thin 
walled ! ) of any capacity from one-fourth to a whole liter, fit it with a 
one-hole stopper and short piece of glass tubing, one end of which has 
been drawn out to a fine opening, and which has been thrust through the 
cork so that the fine opening points into the bottle. 

Pour about 25 c.c. of concentrated aqueous ammonia (sp. gr. 0.90) into 
the flask, insert the stopper with the glass tube, place the flask on an 
iron ring-stand in position to be heated, and clamp or suspend the bottle, 
mouth open and inverted, in such a position that the glass tube from the 
flask extends well into the bottle. 

Warm the liquid gently with a small flame. When it is noticed that 
ammonia is escaping freely into the room, the bottle is probably full of 
the gas. In the meanwhile, secure a pan full of tap-water, and add 6 to 
10 drops of phenolphthalein to it. Then, while keeping the bottle con- 
stantly in a vertical position, raise it until it is "clear" of the glass tube, 
put the stopper with the glass nozzle into the mouth of the bottle, and 
lower it, mouth downward, into the pan of water. What property of 
ammonia gas does the result show? 

Experiment. — (c) Secure two burettes, fill one with dilute hydro- 
chloric acid and the other with dilute ammonia solution. Measure into a 



Chapter VIII 101 

small, clean dish, 10 c.c. of ammonia solution, add one or two drops of 
methyl-orange to it (this is a "neutrality" indicator), and from the other 
burette, add dilute hydrochloric acid drop by drop while agitating or 
stirring the mixture with a clean glass rod so that every drop added may 
be mixed immediately with the rest of the liquid in the dish. When the 
indicator changes its color from yellow to pink, all of the ammonia has 
been neutralized. 

Evaporate the liquid by putting the dish on top of a beaker which is 
just a little narrower than the dish. Fill the beaker half full of tap- 
water, put a piece of wood or paper between the dish and the beaker to 
provide an opening for the steam to escape, and heat the beaker. When 
evaporation on this "water-bath" is complete, note the appearance of the 
solid in the dish, taste it, and finally place the dry dish with its content 
on a clay-triangle, and the latter on a ring of an iron ring-stand so that 
the dish will be in position to be heated. Heat it fairly strongly, and 
note that the white solid — the ammonium chloride — is readily volatilized. 
In this respect it differs radically from sodium chloride, which cannot be 
volatilized except slightly at "white" heat. This difference in the prop- 
erties makes it possible to remove ammonium chloride from its mixtures 
with this or other salts such as the chloride of potassium, magnesium, 
calcium, strontium and barium. 

The "white cloud" observed when ammonium chloride is volatil- 
ized consists of fine particles of the salt in the solid form which 
are formed as soon as the gas is cooled. 

Ammonium chloride is also formed by direct union of ammonia 
gas (NH 3 ) with hydrochloric acid gas (HC1), according to the 
equation — 

NH 3 +HC1^:NH 4 C1. 

Since these two gases are formed extensively, by vaporization, 
from their concentrated solutions, this formation of NH 4 C1 from 
its gaseous components is readily shown by putting a few drops 
of concentrated ammonia solution into a beaker, dipping a glass 
rod into some concentrated hydrochloric acid, and lowering the 
dipped end of the rod into the beaker. Try it. 

Ammonium salts exhibit appreciable dissociation into NH 3 and 
the constituent acid which, as in all such dissociations, increases 
with rise of temperature. Ammonium bicarbonate dissociates 
even at ordinary temperatures so that it gives out an odor of 
ammonia. Slight warming increases the odor very much. When 
ammonium chloride is heated, the odor of ammonia is not ob- 
served because HC1 also is volatile, and the cool mixture which 
strikes the nose contains only N"H + C1. But if we use an am- 
monium salt composed of a non- volatile acid (e. g., ammonium 
sulphate or phosphate), then we may become aware of the dis- 
sociation which takes place on heating because the NH 3 gas alone 
will be vaporized. 

Experiment. — (d) Put a little ammonium carbonate into a small 
dish, note its odor, then warm it and note the odor again. Try some 
ammonium sulphate in the same way. Write the equation for the disso- 
ciations of these two substances, respectively, including therein the addi- 
tional dissociation of H 2 C0 3 into H,0 and CO,, but leaving H 2 S0 4 intact. 



102 ffOCHl IXTBODUCTOBI' ChEATISTBY 

12. Nitrogen in Its Relation to the Members of Its Peiiodic Group. 

Xitrogen appears as the type element of Group V in the Peri- 
odic Classifies and closely related with it are the 
elements phosphorus, arsenic, antimony, and bismuth, the atomic 
weigh"- gradually rising from X=14 to Bi='208. Again, 
in this family or .group of elements, we have a gradual transition 
from the non-metallic (the lighter elements) to the metals 
heavier elements ). Nitrogen and phosphorus are typical non- 
metal- :. ra : ":imony and bismuth are quite 
metallic in nature or base formers. The intermediate arsenic 
ooth non-metallic and metallic properties: hence it is 
frequently called a metal' 

mr of the elements of this group form similarly eonstr 
compounds with hydrogen* XH, (ammonia). PH., (phosph 
AsH 3 (an 3 '.e of th 

ammonia and the least stab! is si . The stability of these 
hydrogen compounds decreases with the increasing atomic weight 
of the group elements. The bismuth hydride is too unstable to 
form under workable conditk: 

All the elements of this group unite with the halogens (chlo- 
rine, for example), forming compounds having the following 
formulae : 

- .and Bi 

These compounds also exhibit a gradation of properties, especi- 
ally in stability: nitrogen trichloride is an extremely unstable 
liquid which decomposes with explosive violence under the least 
provocation, while bismuth trichloride is a ble solid. 

The elements of this group also form similar oxides, a typical 
series beinsr 

- -. and E 

The study of the oxygen compounds of nitrogen will be 

for a later chapter, for the cos I ons underlying this study 

are too complex to be understood by the student nc 

13. The Fundamental Relation Which Brings About the Metathe- 

tical Reactions Between Ammonium Salts and Strong Bases. 

Experiment. — Put some dry ammonium chloride into each of two Test- 
tubes; do the same with ammonium sulphate: add to one portion of am- 
monium chloride and to one portion of ammonium sulphate a little sodium 
hydroxide solution, and to the other portions some slacked lime and a 
few drops of water. Warm the mixtures and note the evolution of am- 
monia. These mixtures first react metathetically to form XILOH. and 
then this substance dehydrates. Write the equations. 

14. Exercise. 

1. Point out the fundamental relation which brings about a 
metathetical reaction between any ammonium salt and any strong 
base. 



Chapter VIII 



103 



2. What equilibria are present in an aqueous solution of am- 
monia ? 

3. Write in proper order the equations for the reactions that 
take place when ammonia gas is absorbed in dilute sulphuric acid. 

15. The Properties of the Halogens, the Elements of Group VII. 

The four elements, fluorine, chlorine, bromine, and iodine, are 
the members of Group VII of the Periodic Classification, and as 
a family of elements they have properties which are either the 
same in all of them, or they differ gradually in the order which 
they appear in the group according to the gradual increase of 
atomic weight (from Fluorine=19 to Iodine=127). The halo- 
gens derive their name from the fact that their sodium salts so 
closely resembles sea salt (which is principally Nad) — the term 
halogen meaning sea salt producers. 

The first two members are gases, the third a liquid, and the 
last a solid; in appearance they pass gradually from a light yel- 
low to a purplish-black. The table below presents these facts : 



Element 


Boiling 
Point 


Physical 
State 


Color 


Atomic 
Weight 




—187° C. 
— 34° 
+ 59° 
+184° 






19.0 








35.5 








79.9 


Iodine 






126.9 











The halogens are extremely active elements, but they exhibit a 
gradual decrease of chemical activity with increasing atomic 
weight. Thus, in the case of their direct union with hydrogen, 
when fluorine and hydrogen are brought in contact, the union 
takes place with explosive violence even in the dark. Chlorine 
and hydrogen, however, do not unite in the dark, but they unite 
explosively in bright light or sunlight. Bromine vapor and hy- 
drogen do not unite even in sunlight, but require the application 
of a flame, while iodine vapor and hydrogen require strong heat- 
ing and a catalyst (spongy platinum) to effect a combination. 
The following thermo-chemical equations express strikingly this 
gradation : 

H 2 +F 2 =H 2 F 2 -f?7,000 cals, 
H 2 + Cl 2 =2HCl+44,000 cals. 
H 2 +Br 2 =:2HBr+16,880 cals. 
H 2 +I 2 =2HI— 12,080 cals. 

All four of these hydrogen halides are colorless gases with pun- 
gent, irritating odors. When condensed at low temperatures or 
under great pressure in the absence of water they form liquids 
with the following boiling points: 



104 Schoch: Intkoductoky Chemistry 

Compound Boiling point (760 mm.). 
H 9 F. +19.5° C. 

HC1 —83.1° C. 

HBr —73.0° C. 

HI —34.1° C. 

It will be noticed that the above boiling point series is not 
regular, the irregular compound being H 2 F 2 . This compound does 
not have the simple formula as the three others, but is double the 
others; i. e., is polymerized. It is a general fact that the first 
member of a group of elements always shows quite a deviation in 
properties from those of the rest of the group. Thus, the com- 
pounds of fluorine often show distinct differences in behavior; 
like the irregularity in the gradation of the group boiling points 
of the hydrogen com pounds. Another irregularity of fluorine can 
be shown in the fact that aqueous solutions of the hydrogen com- 
pounds of all the halogens, except fluorine, are good conductors 
of the electric current: H 2 F 2 is a relatively poor conductor. This 
aberration of the first element of a group has already been pointed 
out in the case of the sixth group, where oxygen in its behavior 
often differs markedly from sulphur, selenium, and tellurium in 
many cases. Oxygen alone of this group forms a halogen com- 
pound of the type C1E_, — i. e., CIO., chlorine dioxide. Then, too, 
its hydrogen compound is a liquid at room temperature, while 
those of the others are gases. 

The hydrogen compounds of the halogens are all very soluble 
in water : 50(5 volumes of HC1 gas will dissolve in one volume of 
water at 0° C. and 760 mm. of pressure. 

Other physical and chemical properties of the halogens and the 
halogen halides will be pointed out in the following articles and 
experiments; attention will also be called again to the exhibition 
of the gradation of properties in the mutual replacing power of 
the halogens. (See Art. 19.) 

16. The Preparation of Chlorine. 

The reactions involved in the preparation of chlorine involve 
entirely different fundamental facts than the metathetical reac- 
tions studied at present, hence the preparation of chlorine really 
does not fit in here. However, it is desirable to demonstrate here 
the properties of the element, and hence its preparation must be 
given. The details of the reactions involved in the preparation 
of chlorine need really not be considered here and the general fact 
alone need be learned that oxidizing agents react with hydrochloric 
acid to give water and free chlorine. The oxidizing agents may 
be considered to be suppliers of oxygen merely, and the oxygen 
they supply reacts with the hydrochloric acid according to the 
following 1 equation : 

0+2HCl=H 2 0+Cl 2 . 



Chapter VIII 105 

The portion of its oxygen which an oxidizing agent may be 
able to give up to be used according to the foregoing equation 
depends "upon the kind of products that the other components of 
the oxidizing agent form simultaneously in such a reacting mix- 
ture, and since we are here not directly interested in learning the 
latter facts, it is really superfluous to consider these reactions any 
further. But since many texts give these extra details, and since 
it will not be amiss to satisfy a student's possible desire for an 
illustration, we will give the details of these reactions with two 
of the simplest illustrations. 

When potassium chlorate is mixed with concentrated hydro- 
chloric acid, all of the oxygen of the chlorate is used up according 
to the reaction above, and the remaining constituents (KC1) re- 
main as a compound by themselves. Hence we have — 

KC10 3 +6HC]=KC1+3H 2 04-3C1 2 . 

When manganese dioxide is mixed with concentrated hydro- 
chloric acid, one-half of its oxygen is used in accordance with the 
reaction — 

0(from Mn0 2 )+2HC1=H 2 0+Clo 
while the remainder (MnO) acts as a base, giving — 

MnO+2HCl=MnCl 2 +H 2 0. 

The sum of these two reactions gives the whole reaction — 

Mn0 2 +4HCl=MnCl 2 +Cl 2 +2H 2 0. 

The substances used in the following test-tube trial all act as 
oxidizing agents with concentrated hydrochloric acid — i. e., they 
give up a fraction of their oxygen to be used according to the 
equation — 

0(from Ox. agent) +2HGI=H 2 0+C1 2 . 

Experiment. — (a) Put into separate test-tubes a pinch of each of the 
following substances: manganese dioxide, lead dioxide, potassium chlorate, 
potassium nitrate, potassium permanganate. Add a few drops of concen- 
trated hydrochloric acid upon each one of these powders and hold the 
test-tubes up to the light to see the greenish yellow gas generated by the 
mixture. Do not inhale the gas! It is likely to produce nausea and in- 
flammation of the lining of the throat. 

Another way to prepare chlorine is to treat bleaching powder — 
chloride of lime, CaOCL, — with an acid. Bleaching powder is 
made by exposing lime to chlorine gas: the two combine to form 
a compound with the formula given above. When an acid is 
added to this substance, reaction takes place in such a manner 
that the lime appears to be neutralized by the acid, and the 
chlorine is set free. Since chlorine is a powerful germicide and 
bleaching agent, bleaching powder is used frequently in daily life, 
and the reaction just described is <?»f great practical importance. 



106 Schoch: Introductory Chemistry 

In the following experiment, the acid used is hydrochloric acid 
and the mixture reacts according to the following equation: 

CaOCl 2 +2HCl=CaCl 2 +H 2 0-fCl 2 . 

Experiment. — (b) (If possible, this whole experiment should be 
done out doors.) Secure the apparatus used for the preparation of car- 
bon dioxide, put a handful of bleaching powder into the flask, moisten it 
with a little distilled water, and when ready to collect the chlorine gas, 
allow concentrated hydrochloric acid to drip slowly upon the bleach- 
ing powder. Secure four wide-mouth bottles of 300-500 c.c. capacity, four 
pieces of glass for covers and a piece of stiff paper or cardboard — about 
3x3 inches: — perforate the latter in the center, slip the conducting tube 
from the chlorine generator through the perforation, and use the card as 
a cover while filling the bottles. Fill the bottles with chlorine and set 
them aside each covered with a piece of glass. 

Dip a little cotton into hot turpentine and thrust the cotton into a 
bottle full of chlorine. Result? Into another bottle sprinkle a little 
powdered antimony. Result? Expose some moist colored calico to chlo- 
rine gas for ten to fifteen minutes. Result? 

Secure a hydrogen generator, attach a glass nozzle to its delivery tube, 
turn on and light the hydrogen gas (small flame!) and project the flame 
into the last bottle full of chlorine. Test for the presence of the com- 
pound formed by this combustion by putting some ammonia solution on 
a piece of filter paper and holding it in the mouth of the bottle. 

To get rid of the chlorine still in the bottles, they may be left, un- 
covered, out doors; or they may be filled with tap-water (out doors!) or, 
a little concentrated ammonia may be added to each bottle, the bottle 
closed with a piece of glass, and shaken vigorously. Ammonia reacts 
with chlorine according to the equation — 

2XH 3 +3C1 2 =N 2 +6HC1. 

The bottles should then be washed, and turned upside down to drain. 

17. The Preparation of Hydrochloric Acid Gas. 

Experiment. — (a) Prepare some hydrochloric acid gas by adding con- 
centrated sulphuric acid to test-tubes containing sodium chloride, am- 
monium chloride, and magnesium chloride, respectively. Try also the 
effect of concentrated phosphoric acid and of concentrated acetic acid, re- 
spectively, on sodium chloride. The formation of hydrochloric acid gas 
may be revealed by holding a glass rod with a few drops of aqueous am- 
monia on it near the mouths of these test-tubes. 

The reactions between these chlorides and acids are all meta- 
thetical reactions, but all the acids act with one H + in the mole- 
cule. Thus, for sodium chloride and sulphuric acid, the equa- 
tion is — 

NaCl+H(HS0 4 )=]SraHS0 4 +HCl. 

This is due to the fact that all the mixtures contain an excess of 
acid, and hence only acid-salts are formed. 

On account of the great solubility of H CI in water, dilute acids 
cannot be used to prepare gaseous HC1. 

Since we know that the reaction in the above mixtures is a 



Chapter VIII 107 

metathetical reaction, the following relation must be true of these 
mixtures : 

[H + ]X[C1-]>[H + ]X[C1-] 
In mixture In resulting 
before reaction mixture 
takes place 

This shows why water must be kept out of the mixture. If water 
were present, there would be many H + and Cl~ ions retained by 
the mixture. It is evident that in the absence of water the mix- 
ture (i. e., the concentrated acid) does not retain these ions. 

Experiment. — (b) Secure the flask and fittings used for the prepara- 
tion of carbon dioxide; put a handful of common salt into the flask, add 
a little water to make a thick mush with the salt, and when ready to 
collect the gas, allow concentrated sulphuric acid to drip upon the salt. 
Collect an ordinary, narrow-mouth bottle (not thin walled) full of the 
gas, and ascertain its solution by thrusting the mouth of the bottle into 
a basin fall of water. 

Note the general resemblance in the kinds of materials used 
for the preparation of C0 2 (or H 2 C0 3 ), S0 2 (or H 2 S0 3 ), and 
HC1: in each case a salt of the desired acid is treated with an- 
other acid. 

18. The Preparation of Hydrobromic and Hydriodic Acid Gases by 
Metathetical Reaction and the Liberation of the Non-Metals 
from Them. 

Experiment. — (a) Put some potassium bromide crystals into a test- 
tube, cover them with concentrated phosphoric acid, and warm the mix- 
ture: to reveal the hydrobromic acid gas formed, dip a glass rod into am- 
monia and bring it near the mouth of the test-tube. What are the fumes 
formed? Then try, in the same way, potassium iodide with concentrated 
phosphoric acid ( and with glacial acetic acid ! ) . Set the test-tubes on 
your test-tube rack. 

From the above trials, and from the experiments of Arts. 1 
and 21, it is seen that a general method for the preparation of 
the hydrogen — halides from the metal — halides is given by the 
statement: treat a metal-halide with a concentrated, non-oxi'diz- 
ing and non-volatile acid. To illustrate why the choice must be 
limited to a non-oxidizing acid, the following experiment is given : 

Experiment. — (b) Cover some potassium iodide crystals with con- 
centrated sulphuric acid, and warm the mixture. What is the coloration 
due to? 

Experiment. — (c) Take the test-tubes (set aside in (a) ) and add a 
pinch of manganese dioxide to the contents of each, and warm the mix- 
ture. What is obtained now? What would have been obtained with 
chlorides? What general statement could be made regarding the obtain- 
ing of the free element of the non-metals from halide compounds? 



108 Schoch: Inteodttctoey Chemistry 

19. A Demonstration of the Mutual Replacing Power of the 

Halogens. 

Experiment. — To a solution of potassium bromide, add some chloro- 
form and some chlorine water; the latter will form bromine by reaction. 
iShake the mixture: the chloroform collects the bromine because the lat- 
ter is more soluble in chloroform than in water. Repeat the whole, using 
potassium iodide in place of potassium bromide. Finally treat some potas- 
sium iodide solution with bromine water and chloroform. 

In these reactions the free element present at first displaces the 
combined element. This power of displacement is in the order: 
chlorine, bromine, iodine. This should be remembered. The 
equations for the reactions are very simple: e. g., 2KBr— I 
2KC1— Br... Write the others. 

The foregoing- experiments are intended to show that in many 
respects the halogens are entirely alike in properties, and that 
their differences in properties exhibit a gradation. The most im- 
portant property in which they show a gradation is their tende-nr-y 
to change from the free element to the form of simple (binary ! ) 
compounds with metals or hydrosren : this tendency is greatest in 
fluorine and least in iodine, with the others in between in the 
order: fluorine, chlorine, bromine, iodine. 

20. The Properties of Fluorine and of Hydrofluoric Acid. 

Fluorine and hydrogen fluoride are. in some respects, markedly 
different from other halogens and other halogen hydrides re- 
spectively: hence the most important differences, or the peculi- 
arities of fluorine. — are to be pointed out here. 

"When CI .. Br, and L dissolve in water they remain unchanged 
except small amounts which react according to the equation — 

X -HOH=HX-HOX. 

but fluorine reacts with water immediately and completely when 
it comes in contact with it, according to the equation — 

of l — ?H,0=2H 2 F 2 -^0;. 

It is on this account that no demonstrations are made here with 
the element fluorine. 

Hydrofluoric acid is notably different from the other halogen 
hydrides in the fact that its solution in water is a weak acid, 
while the solutions of HC1. HBr and HI are strong acids: and 
bv the more striking fact that it reacts with sand, Si0 2 (or with 
glass, which is a fused mass rich in sand or a compound of 
sand), according to the following equation: 

Si0 2 -f ?H ; F 2 :=:SiF 4 ^-2H 2 0. 

This reaction takes place with both gaseous H 2 F 2 or with an 
aqueous solution of H 2 F 2 . In the absence of water, silicon tetra- 



Chapter VIII 109 

fluoride escapes because it is a gas, while in the presence of water 
it remains in the solution. 

21. The Preparation of Hydrofluoric Acid, and the Action of the 

Latter on Glass. 

Experiment, — Mix a little calcium fluoride and concentrated sulphuric 
acid in a test-tube. Warm the mixture and allow the gas evolved to act 
on the sides of the test-tube for fifteen minutes or more. Wash out the 
test-tube., allow it to dry, and then examine it ( ? ) . Note the similarity 
between the preparation of this gas and that of hydrochloric acid gas, 
and hence make your conclusions as to the conditions that bring about 
the metathetical reaction between calcium fluoride and concentrated sul- 
phuric acid. 

22. Practically Important Chemical Properties of Silica and of 

Silicates. 

Pure sand (Si0 2 ) does not react with any acid except hydro- 
fluoric acid; it is not acted upon by any other solutions except 
solutions of strong bases — NaOH and KOH. The action of the 
latter results in the formation of silicates — Na 2 Si0 3 or K 2 Si0 3 , 
which are soluble in water. The action takes place very slowly 
with NaOH solution, but with solid caustic soda which has been 
melted by heating it to a high temperature, the reaction takes 
place in a few minutes, according to the equation — 
2NaOH4 Si0 2 =Na 2 Si0 3 +H 2 0. 

This reaction shows that silica (Si0 2 ) resembles carbon diox- 
ide in its chemical properties. Note the relative positions of car- 
bon and silicon in the table of the Periodic System of Elements. 

Sodium silicate is also formed when sand is "fused" with solid 
sodium carbonate. The following equation expresses tne reaction : 
Na 2 C0 3 +Si0 2 =]Sra 2 Si03+C0 2 . 

In practice, a mixture of equal parts of sodium carbonate and 
of potassium carbonate is employed, because this mixture has a 
lower melting point than either ingredient alone. 

Experiment. — The fusion of sand or silicates with alkali carbonates, 
and the preparation of gelatinous silicic acid. 

Secure about 20 grams of sodium-potassium carbonate and 4 grams of 
sand, grind the sand to an impalpable powder in a mortar, then add the 
NaKCO.,, and grind the two together until they are intimately mixed. 

Secure a medium-sized crucible, cover this with its lid, and place it 
on a clay-covered triangle, — and the latter, in turn, on the ring of an 
iron ring-stand — in position to be heated with a blast-lamp. Secure 
some metal tongs to handle the lid when it is hot. 

Put about one-fifth of the sand and carbonate mixture into the cruci- 
ble, cover the latter, and heat it with a moderate blast-flame until the 
mixture in it has fused to a clear liquid. Then add another portion, use 
it, and so continue until all of the substance has been melted. Then 
allow the crucible and contents to cool, put it into a medium-sized beaker, 
add distilled water until the crucible is submerged, and heat the water 
gently until the fused mass has been thoroughly disintegrated, and the 
crucible is practically free from it. Filter the liquid. The solid residue 



110 Schoch: Introductory Chemistry 

present is undecomposed sand, in the main. The clear solution contains 
the alkali silicate and the excess of alkali carbonate. To the filtrate add 
small portions of concentrated hydrochloric acid, until, after stirring, the 
mixture contains an excess of acid. Test with litmus! Note the forma- 
tion of a white, flocculent precipitate in appearance similar to Al(OH) 3 : 
this is hydrated silica or silicic acid, ILSiOj or H 4 Si0 4 . Evaporate the 
mixture on a water bath, and note that just before the mass became dry, 
it has the appearance of a gelatinous material similar to "cooked sago." 
This is silicic acid. Leave the dish on the water bath until the residue 
is dry: — a white impalpable powder remains — this is Si0 2 , silica. 

23. Compounds of Silica — Silicates. 

A large part of the earth's crust is made up of compounds of 
silica. Many different kinds of rocks, potter's clay, and a large 
part of the alluvial soil is composed of silicates. Among the 
manufactured articles composed of silicates, we have brick, tile, 
pottery, porcelain ware, and glass. All silicates are insoluble ex- 
cept those of the alkalies. The latter, e. g., Na 2 SiO n , mixed 
with water, form transparent masses, which are soluble in water, 
and are known as water glass. 

24. The Melting Points of Silicates — The Most Important Fact 

About Them. 

The fusion of silicates occurs in the fluxing of ores, in glazing 
pottery, in vitrifying bricks, and above all in the manufacture of 
glass. In all of this work, the general fact is made use of that 
mixtures of silicates of two or more metals have lower fusing 
points than their components have separately. — and the fusion 
point of a mixture varies with the proportions of the ingredients : 
with the aid of tables of fusion points of mixtures, the chemical 
engineer has the material put into a furnace in such proportions 
that the mass may fuse at the lowest temperature. 

25. The Analysis of Silicates. 

Most of the insoluble silicates are like sand in their behavior 
with solutions of acids or of alkali hydroxides. In order to ascer- 
tain the bases in them, they must be fused with NaKCO, just 
as the sand was fused above, the fused mass treated with HC1 
and evaporated by dryness. The residue thus obtained from a 
silicate contains chlorides of the bases together with Si0 2 . This 
residue is treated with dilute HC1 and water to dissolve the salts 
of the bases present, the mixture is filtered to remove the Si0 2 , 
and the filtrate is used to find the bases by the regular procedure. 
(Shown in a later chapter.) 

Questions on Chapter VIII. 

1. What is the commercial source of ammonia? What is the 
commercial source of sulphur? What are the allotropic forms of 
carbon ? 



Chapter YIII 111 

2. (a) What chemical changes take place when carbon 
dioxide dissolves in water? (b) What further action takes place 
if this water also holds a base in solution (e. g\, sodium hy- 
droxide) — the base being present in relatively large amount? (c) 
After enough of the carbon dioxide has been passed into the solu- 
tion to change all the sodium hydroxide to normal sodium car- 
bonate, if then the stream of carbon dioxide is continued, what 
further change will take place? 

3. (a) Give the equations for all the reactions if the base 
in (2) were lime, (b) State what would be observed if the re- 
sulting solutions were boiled? Give the equations for this last 
change. (c) Point out where these reactions take place in 
nature. 

4. (a) Show by formulas what is meant by "step dissocia- 
tion" of carbonic acid, (b) When a so-called insoluble carbo- 
nate, such as marble, is acted upon by an acid, the number of 
carbonate ions per c.c. furnished by the dissolution of the marble 
is naturally very small. Since the metathetical reaction takes 
place as with sodium carbonate, there must be a particular com- 
bination of ions which tends to remain so nearly completely com- 
bined that even the small number of carbonate ions from the dis- 
solved marble will be made less by forming this combination; what 
is this combination? 

5. How much carbon dioxide could be obtained by means of 
5 grams of hydrochloric acid ? 

6. Describe how sulphur dioxide was prepared in the labora- 
tory; give the chemical equation for the reaction of the substances 
in this preparation and the properties of this substance which 
have been shown you experimentally. 

7. Write in proper order the equations for the reactions that 
take place when sulphur dioxide is absorbed in an excess of sodium 
hydroxide. If the addition of sulphur dioxide is continued be- 
yond the point of neutralization of the sodium hydroxide, what 
new reaction will set in? Give the equation for the latter. 

8. Mention the elements known as the halogens. In what re- 
spects are they alike ? What is the order of their atomic weights ? 
of their physical appearance, and of their tendency to form sim- 
ple compounds with hydrogen or with metals ? How was the lat- 
ter demonstrated to you experimentally? 

9. How was chlorine prepared from hydrochloric acid? Tell 
what you know concerning this reaction. State briefly the prop- 
erties of chlorine that you have become acquainted with in the 
laboratory. How does hydrofluoric acid act upon glass or sand? 
Give the equation of this reaction. 



- :- : " 



:~ - ?rzj ::: 
:::^::i weights op xoixctjijbs. 

' ■ • 

. . - - - - ' :. -..:; 

gasef :~nrre and behaTior on-timed in Chap- 

: 
tlUj _ •ompiwpd of a fixed number of atoms. A etc 

:i-. :•:•:: IrH-Enc : _- >— - 1. - : - . - :-•-..--.•' _-. - r :-ir.:l-- 

nns are pneticaDj idenn- 
cal t TnlfraW of the gases from winch Hier are con- 

densed. Hence the determinatioii of the number of atoms in tiae 

_ astfied suhrtancpw gincs m a knowi- 
f peaeticalhr all foams of 




■ — ' 

— al Tclxzmes of : The san* 

- - • .. - 

- 

•gen at 0° C and 

?-"•' ^r_ -r:rl= - "" _"::_- : :. 1 : .::■:: : "--- lir-: : - 
- r. - : \: r.= ~ ■ _:- 1.-1 _- :..- :: - — - : - :_ - - i_~:i 

■ 
zzxdecoles — whieh nnmber we denote by 
r need t real YaJoe!} — then one molecule «:: 

. ■ — . 

3 : - - 

ren. Or. in other 
voids, the molecular w ~ 
zl! - : 

. _ : i -- 

- _ . - . - ■ :--r — r 

i - -■=■ : r. : - ' - : - ~- - - — ; - " 

the foregoing we nmsi ^r::zrr the molecular weir :r_- 

=- -- .i .- : - ■ -' - ■ - ; ~~i —~1 r. - "1: - ..- ll-E -"- 

--: -- = :: "1:51-: 



Chapter IX 



113 



Early in the nineteenth century, Gay-Lussac, a French scientist, 
observed that, at the same temperature and pressure, two volumes 
of hydrogen unite with just one volume of oxygen, no more, no 
less; that one volume of chlorine gas units with just an equal vol- 
ume of hydrogen, etc.; in other words, he observed that gases 
which reacted chemically do so in simple volume ratios. The fol- 
lowing experiments are intended to acquaint the student direct 
with this simplicity of these volume relations : 

Experiment. — (a) To Demonstrate the Ratio by Volume Between 
Oxygen and the Sulphur Dioxide Formed From It. 

The apparatus to be used in this experiment is shown in the accom- 
panying figure. Some heavy petroleum or lubricating oil is poured into 
the measuring cylinder; the test tube is detached and filled with oxygen 
(by displacement of air) and a little piece of roll sulphur is dropped 
into it. It is then attached again. Some of the oil is now drawn out 
of the cylinder so that, when the enclosed gas expands later on the oil 
will not flow over the top of the cylinder. Note where the level of the 




oil is within the tube, then heat the sulphur cautiously: when the sulphur 
burns, the enclosed gases will expand, but on cooling they will contract 
until the level of the oil is again at the place at which it was before the 
•sulphur was burned. This shows that sulphur dioxide occupies the same 
volume as the oxygen from which it is formed. 

Experiment. — (b) To Demonstrate the Ratio by Volume in Which 
Oxygen and Nitric Oxide React. 

The instructor will furnish the oxygen and the nitric oxide for this 
experiment. 

Each student should fill, over water in a large pan, a test-tube nearly 
full (not quite full) with nitric oxide gas. and another test-tube nearly 
full of oxygen gas. Mark, with rubber bands, the position of the sur- 
face of the water in both test-tubes. Then transfer a small amount of 
the nitric oxide to the oxygen test-tube, by tilting the former with its 
mouth under the latter. Nitric peroxide will be formed immediately, but 
will dissolve in the water gradually. The whole of the nitric oxide 



114 



h: Ixteoduc toey Chemistby 



should be transferred gradually to the oxygen test-tube. When the eol- 

-1 of the latter does 

mark this final position of the water with another 

a band. Empty t: nd. by means of water drawn from a 

. ime of the nitric oxide used, and of the oxygen 

of the remaining \ The ratio by volume 

in which nitric oxide reacts with oxygen will thus be found to be 2:1. 

Experiment. — [e 7 -trctc th* v Volume 'Between 

Ammonia Gas and It. 

apparatus to be used is =hown in the accompanying figure, except 

uld lead from th-r top of the 

dryir. :' leading to the bottom of the drying tube — 

wn in the figure. The drying tube or -hould be at le 

cm. in length, and 3 to 4 cm. in diameter. It sh »uld be filled with lumps 

•ead of the burette shown in the figure. 

- tube 1 cm. in diameter and f>0-80 cm. in length may lie employed. 

The r Pping funnel, and - i for the ends 

5 ~cial attention must 1* given to this 




point. Concentrated aqueous ammonia is put into the flask, and a small 
name is applied to it. When enough ammonia has passed through the 
apparatus and burette to have swept out all the air. then the stop-cocks 
at the ends of the burette tube are closed. 50 to 100 c.c. of a "warm" 
concentrated solution of chloride of lime is then prepared and poured 
cautiously through the funnel into the burette, care being taken not to 
let air enter or gas leave the burette. 

When no more of the liquid is drawn into the tube the stop-cock is 
and the burette is laid aside until it has cooled down to the tem- 
perature of the room. Then the lower stop-cock is opened ichik this 
end is under xrater : thv. - - within the burette is made prac- 

tically the same as the atmospheric t: - then seen that the 

nitrogen in the tube occupies iust one-half the volume occupied by the 



Chapter IX 115 

ammonia from which it was formed. The chlorine in the chloride of lime ' 
combined with the hydrogen of the ammonia and left the nitrogen free. 

The next step in the development of this subject was the recog- 
nition that this simplicity of the volume relations between the 
amounts of gases used up or formed by chemical reaction, — that 
these simple relations establish simple relations between the num- 
bers of atoms in the molecules of the gases involved in the same 
reaction. Thus, the result of the first experiment above shows 
that there are as many atoms of oxygen in the molecule of sul- 
phur dioxide as there are in each molecule of oxygen. (Why? 
Employ Avogadro's law in your consideration.) Again, the re- 
sult of the second experiment shows that there must be at least 
two atoms in the molecule of oxygen because since two volumes 
of nitric oxide combine with 1 volume of oxygen, 2 molecules of 
nitric oxide use up 1 molecule of oxygen, and each molecule of 
nitric oxide receives the contents of one-half a molecule of oxygen: 
hence, the oxygen molecule must be divisible into two equal parts — 
i. e., it must contain 2 atoms or a multiple thereof. 

The third experiment shows with its volume relations that the 
total number of ammonia molecules in the tube form one-half as 
many nitrogen molecules, and since one atom is the least amount 
of nitrogen that each molecule of ammonia can contain, it follows 
that each molecule of nitrogen has received at least 2 atoms. 

The same argument applied^ to similar experiments has shown 
that hydrogen, oxygen, and chlorine, also, have at least two atoms 
in their molecules. 

But there is no reason why this number of atoms in the mole- 
cules of these gaseous elements should be greater than two : hence 
for simplicity's sake we shall consider it to be a settled fact that 
the number of atoms in a molecule of these gaseous elements is 
only two. 

The latter definite conclusion gives us the desired molecular 
weight of at least one substance — hydrogen — because with two 
atoms in the molecule, and with the atomic weight of hydrogen 
known to be 1 — (because we made it the unit of atomic weights), 
two must be the molecular weight of hydrogen. 

3. The Procedure for Obtaining' Molecular Weights. 

The preceding paragraph gives us the following general rule for 
the determination of the molecular weight of a substance: ascer- 
tain the weight of any definite volume of the substance in gaseous 
form at any temperature and pressure that may be convenient or 
necessary, reduce this by calculation to the weight of 1 liter, at 
0° C. and 760 mm., divide this result by the weight of 1 liter of 
hydrogen under the same (standard) conditions (what significance 
has this resulting number?) and multiply the result by 2 (or more 



- 1 : S z : '. 

aocnratelT bx 2.016. because the atomic idgU 

really 1.008 i. 

ProbU- and under TOO mm. 



7L-.7 : ./..v.".:t l :: :_ •■.•.:.: - j -- .- -. :. -ii: z-.rr ?.~- 

;.- • : -•. ::._.-.:._- ; : -. . : > ~: . :. :: ., >izit .: iji: j-.l 
which will contain as many sxanv 

; :— j-t ; ::? :: :.- . .. : - - ' — :ii: :«■. :■ . -. \ . '-■'. > - ^ 
■ - _ -. - . - - . . : . 

z-z:'.-.: : ~ :>:_.-- : : - !"ir_t i: - - -. ?-: ;-:z\L~ .:« --. 
:.;.-•: ::.: ::"J:~:r.j j-.i-r..l ref-.: : _ - n grams .: 52.4 

liters of any gas at and 760 miL - umber which ex- 

€rf Vl 



- 

volume; e. £.. E ut the element of the 

- - - - 

z_ :.:-— -.'. v.::.. ::-.-.: . ;.r_- i. 1:7; : z.. ItZll. n : 1 — - rr. 
z: :•.--■ 1: r .f. - ■ -:..-. :"; - : ?.: : > ..--••..:-: >. -;::t:> ? t t;.: 
: 

- - - -. 

- • - - ' . - 

_:. r v ■:-.■■"".-. : :; - - -:_--.--: : :i- j :- :: ---::: - 
-:::..::•: z 7r £T Tfr -"•". A~ ..: :-:;;-'. ":-■; - : Liz \ 

arsenic and phosphorus at eorrafipnoding tempentz ?tra- 

: • - - - - - : - - - 
...... ...... 

In contra distinction to elements, most gaseoas compounds have 



yi:.~:- 



'- z^z rir ::7r_ _ _ - - 

U:i :ji- -■'-■■-t.-.' '•:.". e:_ ? ~.> l~:- ; : : il~ ~-=:j 
lis :' -. :- " : - i~- : :; -. - ■'.-;:: - : zn " 
the equation. The coefficients of the molecules 

r>: : - - — f - : ~ :: - 







Chapter IX 


117 


2H 2 + 

2 vol. : 


2 = 

1 vol. 


: 2H 2 
: 2 vol. 


(steam) 




s + 


0- = 
1 vol. 


: SO, 
: 1 vol. 


(See Exp. 


(a) above.) 


c + 


2 = 
1 vol. 


: C0 9 
: 1 vol. 






2C + 


2 = 

1 vol. 


: 2C0 

: 2 vol. 






2NO + 
2 vol. 


0„ = 
1 vol. 


= 2N0 2 


(See Exp. 


(b) above.) 


3C1 2 + 2NH 3 = 
In solution 2 vol. : 


= ST 2 + 6HC1 
1 vol. In solution. 


(See Exp. (c) above). 



118 Schoch: Introductory Chemistry 



CHAPTER X. 

THE ACTIONS AND USES OF GENERAL REAGENTS EOR 
SOLUTIONS OF SALTS. 
1. Introduction. 

There are some substances which react with -alts ior many 
metals and which are employed to produce desired combinations 
of ions or to establish the presence or absence of various metal 
ions in solution: such substances are called general reagents. 
Since the reactions which most of the common reagents undergo 
with salts of the common metals are metathefieal reactions, they 
can be understood fully by the student in this period of his 
progress in chemistry, and the action and use of these reagents 
may be studied here with profit. 

Although a general knowledge of the solubilities and degrees 
of ionization oi these reagents and of the vari< - ounds of 

the metals enables one to foresee many of the reactions that could 
take place between them, yet there are some reactions which can- 
not be foreseen because they involve a more accurate knowledge 
of solubilities and degrees of ionization or of still other special 
facts. Some of this more accurate knowledge of solubilities, of 
degrees of ionization, and of other special facts form- asential 

part of chemical information, and is th given in this 

chapter. 

In the selection of the facts, experiments and exercises of this 
chapter, the salts of the following metals are considered : 

Hg+, Hg* -. Cd- ♦ Pb- " 

Cir -. Bi + - -. Al- - ~. 
R- - . Fe+* Ni< -. 



. Mn-~. Ca*". Sr« * 
Ba~ -. Mir -. K-. Xa~. NH 4 



SODIUM (OR POTASSIUM) HYDROXIDE AS A REAGENT. 

The following statement of General Facts and Table of Results 

of Action of Sodium Hydroxide should be read over once; then 
the operations in the exercise should be carried out very carefully 
arid completely with one of the salt solutions : then with another 
<alt solution, etc. Two objects are to be attained through the ex- 
perimental operations : neat and correct manner of handling ap- 
paratus, and a definite knowledge of the appearance and behavior 
of the precipitates, etc. The latter should he committed to 
memory. 

2. General Facts. 

By strict metatlietical reaction, the mixing of sodium hydroxide 
with solutions of salts of all metals except those of which the hy- 



Chapter X 119 

droxides are soluble should give a precipitate of the metal hy- 
droxide— e. g., CdCl 2 +2XaOH=Cd(OH) 2 +2XaCl. However, 
in many eases the substances finally obtained are not the hydrox- 
ides of the metals but substances derived from them through 
one or both of the two following additional changes : 

(a) Dehydration, — complete: Hg(OH), to HgO ; or partial: 
Cu(OH) 2 to Cu 3 2 (OH) 2 . 

(b) Dissolution of the precipitated hydroxide by excess of the 
reagent, which shows that the precipitated hydroxide functionates 
as an acid; e. g., Zn(0H) 2 dissolves in excess of ISTaOH solution 
as per equation ; 

H,Zn0 2 -flS T aOH=Na 2 Zn0 2 -f2H 2 0. 

The formula for zinc hydroxide is thus written to suggest its 
functionating as an acid. 

3. Results of the Action of Sodium (or Potassium) Hydroxide Upon 
Aqueous Solutions of Salts of the Common Metals. 

Ba ++ — Ppt. Ba(0H) 2 : Is precipitated only from concentrated 
solutions because it is soluble one part in 20 parts of water; when 
precipitated : white. 

Sr ++ — Ppt. Sr( OH), —white: Soluble 1 part in 60 parts of 
water; not precipitated from dilute solutions. 

Ca ++ — Ppt. Ca( OH) .—white: Soluble 1 part in 700 parts of 
water; not precipitated from very dilute solutions. 

Mg ++ — Ppt. Mg ( OH ) 2 — white: Soluble 1 part in 6000 parts 
of water. 

Al + + + — Ppt. Al(OH) 3 — white and gelatinous: Soluble in excess 
of reagent, forming NaAK),, an aluminate. 

Zn + + — Ppt. Zn(OH) 2 — white: Soluble in excess of reagent, 
forming Na 2 Zn0 2 ; a zincate. 

Pb ++ — Ppt. Pb(OH) 2 — white: Soluble in excess of reagent, 
forming ^~a 2 Pb0 2 ; a plumbite. 

Fe ++ — Ppt. Fe(OHV>- — white when pure: Darkens on exposure 
to air (oxidizes partially to ferric state). 

Fe + + + — Ppt. Fe ( OH ) b — reddish brown and flocculent. 

M n + + - Ppt. Mn(OH) 2 — "flesh" colored: Darkens on exposure 
to the air (oxidizes partially to manganic state). 

Ni ++ ~ Ppt. Xi(0H) 2 — pale green. 

Cu ++ — -Ppt. Cu(OH) 2 — bluish white: Soluble in large excess 
of reagent; in hot solution it is dehydrated, forming CuO, a black 
ppt. 

Cd + + — Ppt. Cd (OH) -- white. 

Bi + + + — Ppt. Bi ( OH ) .,— white. 



1 - - 

Er — 7 " Egj — black: r 

salt 

■ 

- : ~ T . 

t 
. 6 . B . 

cubic u irtiw tors of each of these solutions in a Te?=T-Tube. add 
8 few ir | xide wHntion. shake each mixture and note 

ew dropf 

•en added in i mm. say. 

about Twice as much reagent br volume as 

ent concentrations C oteth .- ■ 

' .ke a 

-•agent and pive all equa- 

p next opera ti ^ 

: 
aohrt a dilute acir add 




■ 
dread: acid deex pexnatrat liquid as 

: 
iimfl am e acconr i -: 

id another raount 

dt mean? of the least tiuwiMt 

—aride dissolved ir< exc r wide, 

I 

: 

- - . - . - - _ - 

- " roei i i "~ 



Chapter X 121 

The action of the acid upon this solution requires some ex- 
planation. The dissolving of a metal hydroxide in excess of sodium 
hydroxide is a reversible reaction, which is forced to completion 
by the presence of more sodium hydroxide than is used up in the 
reaction: when an acid is added to such a solution the excess of 
sodium hydroxide is done away with (equation?) and the reversi- 
ble reaction in question then takes place simply in the reverse 
direction from that in which it just took place, and the precip- 
itate reappears. Thus when an acid is added to a solution of 
Na^ZnO.,, the following reaction takes place gradually as the 
excess of NaOH is diminished: 

Na 2 Zn0 2 -f2H 2 0±^2N T aOH+Zn(OH) 2 : 

Note. — The student should try to remember the color and 
general appearance of each solution and precipitate handled. 

5. Illustrations of Various Uses of Sodium Hydroxide as a Re- 
agent. 

(a) To remove a metal ion completely from a solution: 
When enough sodium hydroxide has been added to a solution of 
a "ferric" salt to change all of the Fe + + + ion to Fe(OH) 3 , and 
the precipitate has been allowed to settle, then 'the addition of a 
drop more (which is generally spoken of as an excess) will not 
produce a change, and the fact that all of the Fe + + + ion has been 
precipitated is indicated by the fact that the upper, clear part of 
the solution will remain clear on the addition of this extra drop 
of sodium hydroxide solution. Would all this apply as well to a 
solution of an aluminium salt? Hence, for which metals only 
may sodium hydroxide be used as a precipitate ? See table above. 

(b) As a separating agent. This will be illustrated with the 
following experiment: 

Experiment. — The Separation of Copper from Zinc (from brass). 
Dissolve small amounts of brass pieces by placing them in a small evap- 
orating dish, and adding the least amount of a mixture of concen- 
trated nitric acid plus an equal volume of water which will dissolve 
them. Put the dish on an improvised water bath, and evaporate the 
contents to dryness. Add a few c.c. of distilled water to dissolve the 
salts in the dish. Then place about 15 c.c. of sodium hydroxide and 
about 45 c.c. distilled water into a beaker and heat the contents to boil- 
ing. Into this boiling solution add the solution from the dish, a little 
at a time with constant stirring, until all has been added. Enough 
sodium hydroxide should be present to have precipitated all the copper 
as copper oxide and to have dissolved the zinc as sodium zincate. 
Allow the copper oxide to settle, and decant the liquid into another 
beaker. Add water to wash the copper oxide free from the adhering solu- 
tion ; then decant and discard this wash water. Wash the copper oxide 
a second time in the same manner; then dissolve it in the least amount 
of dilute sulphuric acid, and evaporate the solution to such an extent 
that copper sulphate crystals will separate from it on cooling. 






TXTBODU 



Into the solution in the other beaker drop a piece of litmus paper, add 
a few drops of hydrochloric u be mirture. add a few drops more 

and so continue until the litmus indicates that the solution is neutral. 
Most of the zinc hydroxide will then have been precipitated. Decant as 
much of the liquid as possible, then pour it upon as large a filter paper 
:he accompanying sketch for method of folding filter 
paper, and for correct manner of pouring liquids on filter papers^ 
a wooden funnel stand: the ni*f from iron liable to drop into 

the filtrate. When uk - iquid has been removed by filtration, 

transfer the contents of the filter to a small dish, add concentrated hv- 





Filfer 



*~z z e z : - ze 





rolded twice Opened 

Directions for folding filter paper. 





Correct flterinj. 



Incorrect Filtc- -§ 



drochlorie aei<L a few drops at a time, until the zinc hydroxide has dis- 
solved. Then evaporate the solution until everything that is volatile has 
been expelled. A molten residue of zinc chloride will remain. Select, 
from the table above, other pairs of metals which may be separated in 
— av bv means of sodium hvdroxide. 



The following experiments make nse of the same facts aiid prin 



Chapter X 123 

ciples as the foregoing, but they employ the cheapest soluble hy- 
droxide that occurs in commerce, and they illustrate two very im- 
portant industrial operations. They are also intended to teach 
the student correct chemical manipulation. 

6. The Old Commercial Preparation of Sodium (or Potassium) 
Hydroxide. 

Weigh out roughly 25 grams of anhydrous sodium carbonate or 67 
grams of crystalline Sal Soda (Na 2 C0 3 . 10ELO) , place it into a large 
porcelain dish, add about 250 c.c. distilled water, and heat the solution 
until it boils. In the meanwhile calculate how much slaked lime would 
react with this amount of sodium carbonate; then calculate how much 
quicklime would be necessary for this much slaked lime; then weigh 
out roughly one and one-half times as much quicklime as calculated, place 
it into a small dish, add distilled water to slake it (warming the dish, 
if necessary, to start the action), and then add enough water to make 
the lime into a thin paste. Pour this paste gradually, with stirring, 
into the boiling soda solution. (Care should be taken to have the vol- 
ume of the boiling soda solution about 250 c.c. ) . What reaction takes 
place? Continue boiling for a few minutes — Why? Pour the mixture 
into the smallest beaker that will hold it, and allow it to settle. 

In the meanwhile secure two burettes, and fill one with normal sul- 
phuric acid (N H 2 S0 4 ). Fill the second burette with some of the clear 
part of the sodium hydroxide just prepared. Measure out accurately 10 
c.c. of this into a beaker, dilute with water, add a drop of an "indicator 
of the point of neutrality" (methyl orange) and titrate with the normal 
sulphuric acid. Xote the number of c.c. of the normal sulphuric acid 
used. By means of a measuring cylinder, measure the volume of the 
sodium hydroxide solution (without the main part of the sediment). Be 
sure to drain the liquid well from the sediment — the total volume of the 
sodium hydroxide solution should include the amount in the burette plus 
the 10 c.c. used for titration. 

In order to ascertain the amount in grams of sodium hydroxide 
obtained, answer the following questions and make the calcula- 
tions indicated: 

(a) How many grams of sulphuric acid does 1 c.c. of a nor- 
mal sulphuric acid solution contain? 

(b) How many grams of sodium hydroxide will this weight 
of sulphuric acid neutralize? 

(c) The number of c.c. of normal sulphuric acid used for 
titration multiplied by the number of grams of sodium hydroxide 
neutralized by 1 c.c. gives the number of grams of sodium hydrox- 
ide in the 10 c.c. sample. Make this calculation. 

(d) What fraction of the total volume of sodium hydroxide 

1 
was the 10 c.c. sample? Multiply the result of (c) by — , where 

X 

X= fraction of whole which 10 c.c. equals. This gives the total 
amount of sodium hydroxide produced. 

(e) Compare this amount with the amount of sodium hy- 



hock: I^tsoductohy Chesostsy 

. - : calcnlatwB, should have been obt: 
m carbonate 
In your nc lppens in ea.: ~ .doa, and 

_~ A Hrwi elation is such a solution which con- 

nnmber of :irams numer. 
eqna. I 

; . normal soln- 

3 — ' 

•vial sole 

- - 
phnr: ~vo replaceah 

" - 
■ 

! 

rram 

- ■ ■ " --: 

=58 

A normal soLrr issimn sulph 

Intions are mostly designated b~ 

- 

rmal by t&. It 
: 

is strong as a normal solution. 

phnr. It w - - --__■;- QTL ± 

sulphuri 7 normal 

tion 

tains B - " '. 

j s 

= : ' ". ■ ■ --raid cor. fca " . " : B - \ 



Chapter X 125 

Further, the statement can be made that 1 c.c. of a normal sul- 
phuric acid solution is equivalent to 1 c.c. of a normal sodium 
hydroxide solution. Why is this true? The equation for the 
reaction is 

2NaOH+H,S0 4 =:]\ T a 2 S0 4 +2H 2 
2(40) + 98 

In words, 2X40 grams of sodium hydroxide react with 98 grams 
of sulphuric acid — or 40 grams with 49 grams of sulphuric acid. 
One liter of normal sodium hydroxide solution contains 40 grams 
per liter and one liter of sulphuric acid contains 49 grams of 
acid. Hence it is seen that 1000 c.c. of N" NaOH neutralize 1000 
c.c. of a N H 2 S0 4 solution or 1 c.c. of N NaOH=:l c.c. of N. 
H 2 S0 4 . 

HOW TSTOEMAL SOLUTIONS ARE PREPARED EROM STOCK. 

(a) Normal Sulphuric Acid: Eequired 49 grams of pure 
H 2 S0 4 per liter of solution. Use C. P. sulphuric acid of sp. gr. 
1.84, which is 96% pure. Use an accurate burette and measure 

49 

out = 27.74 c.c. into a liter flask containing about 

0.96X1.84 

200 c.c. of distilled water and then add distilled water so that 
the solution, when cooled to 20° C, comes to the 1000 c.c. mark 
on the neck of the flask. This gives very nearly a normal sul- 
phuric acid solution, which may be used (without further stand- 
ardization) for all but the most accurate work. 

(b) Normal Potassium Hydroxide: Eequired 56.1 grams of 
pure KOH per liter of solution. Use KOH sticks, "purified by 
alcohol," which contains about 88% of KOH. The amount re- 

56.1 

quired will be = 63.75 gms. Weigh out this amount and 

0.88 

place into a liter volumetric flask and add distilled water so that 
the total solution, when cooled to 20° C, is just 1 liter. This 
solution will in all probability not be exactly normal, since the 
purity of KOH sticks is not always 88%. The resulting solution 
should be titrated against a normal acid and a "factor" used. 

(c) Normal salt solutions can be made by weighing out the 
required amount of salt (taking into account its purity and the 
water of crystallization) and adding distilled water to make up a 
liter of solution ! 

8. The Commercial Purification of Crude Salt. 

Crude salt contains small amounts of calcium and magnesium chlorides 
and sulphates. The removal of these and of very small amounts of other 



1'26 Schoch: Introductory Chemistry 

impu.- complished as follows in commerce: — weigh out rousrhly 

dissolve it in 350 c.c. of cold water. Put the 

solution in a flask, and add about 10 - iium hydroxide solution. 

the mixture to boiling and filter it through a large" pleated filter (in 

a 4-ineh funnel | . Add another drop of sodium hydroxide to ascertain 

if enough - — U not. add more and filter again. Then 

-he mixture a_ g 1 about 6 irium chloride 

solution to the hot mixture, allow the precipitate to settle out of the 

top layer and ascertain by an additional drop of Bad, whether 

or not enough of this - m added — if necessary add more Bad. — ami 

stir the mixture to distribute this new portion of reagent over the whole 

solution. gain to find 'isrh BaCl. has been added, and if 

- this whole operation Then, without filtering, add about 

• - lutnm. Ascertain, as before, that eno;. 

this precipitant has been used, then filter through a fresh pleated filter. 

Heat the clear filtrate and add dilute hydrochloric acid, a few drops at a 

time, until after stirring i ith litmus paper it is found that 

- >een neutralized. 
Put the solution into a large clean dish, place this on a wire gauze, 
and heat it with two burners to concentrate the solution as rapidly as 
k until it is in the form of a thin mush: — then pour it quickly on 
a large, smooth filter in a funnel. 

m. — Do not use metal tongs in handling hot beakers or di- 
:hem with the rineers on the extreme upper edge, place them quickly 
on a towel, and then handle them by the aid of the towel. 

In the not' I reagent does _ • the 

^n. Als si why the rapid evaporation and crystalliza- 
tion is necessary : and finally point out how the last traces of im- 
purities in the solution are disr - -or separated from the salt. 

9. Ammonia as a Reagent. 

solution of ammonia contains OH" 
ion. its action on solution - the common metals might 

be expected to be similar to the action of sodium hydroxide. How- 
ever, it differs from sodium h' n several respects: H - 
weal' base (slightly ionized \), while sodium hydroxide is a strong 
- the ion> and their combination, ammonia con- 
tains a srreat many XH : molecules, while sodium hydroxide con- 
tains nothing that corresponds to this NH,. Hence it is not sur- 
prising that ammonia in its action as a reagent is. in general, dif- 
- from sodium hydroxide. 
The first, and most important, difference between sodium hy- 
droxide and ammonia is the fact that ammonia, in the presence 
of its own salts, acts differently in many cases from the way it 
lets in their absence — while sodium hydroxide is not noticeably 
affected by the presence or absence of its own salts. Since an 
ammonium salt is always produced when ammonia lets is a re- 
agent, we need only consider the effect upon other salt solution 
of ammonia mixed with one of its own « 



Chapter X 127 

10. Effects Produced by the Addition of Ammonium Chloride and 
Ammonia to Solutions of Salts of Common Metals. 

Na% K + , Ca + + , Sr + + , Ba + + : — no effect whatever because the 
hydroxides of these metals are strong bases. 

Ag + : — forms a ppt. of AgCl, which is dissolved by ammonia 
to form Ag(NH 3 ) 2 Cl. This compound tends to dissociate into 
its original constituents — 

Ag(Jm, ) ,C1 ^± AgCl-f-2HN 3 , 

and it is stable only in the presence of free NH 3 . Hence, when 
the excess of N~H, in these solutions is neutralized by the addition 
of an acid to the mixture, the insoluble AgCl is obtained again. 

Pb + + : — forms a ppt. of PbCl 2 , and this is changed by ammonia 
to Pb(OH)Cl, an insoluble white compound. 

Hg + : — forms a ppt. of Hg 2 Cl 2 , and this is changed by am- 
monia to a Hack, insoluble mass, admixture of mercury and of the 
compound HgCl NH 2 , according to the equation : 

Hg 2 CL+2NH 4 0H=HgClNH,,+NH 4 C]+Hg+2H 2 0. 

Hg + + : — gives, on the addition of ammonia, HgClNH 2 , a 
white compound insoluble in water. Treated with HC1, it forms 
HgCl.+NHjCl, which are soluble. 

Cu + + , Cd + + , Zn + + , M + + : — they form soluble compounds of 
the general formula M(KrL) 4 Cl 2 

Or M(NH 3 ) 4 S0 4 . 

The cations of these salts are: Cu(NH 3 ) 4 + + , Cd(NH 3 V + , 
Zn(NH 3 ) 4 ++ , M(M ; ) 4 ++ . With colored salts— such as those 
of Cu + + and Ni + + — the formation of the complex ions shows it- 
self by a great deepening of the color.' 

The ammonia compounds tend to dissociate into their original 
constituents — 

Cu(NH,) 4 S0 4 ±^CuS0 4 +l:NH 3 , 

and they are stable only in the presence of free NTE 8 . Hence 
when the excess of NH 3 in these solutions is neutralized by the 
addition of an acid, the original simple salts (e. g., CuS0 4 , in 
the illustration above) are obtained again. 

Fe + + and Mn + + : — these cations are not affected directly by 
N"H i Cl-j-NH 4 0H, but in alkaline solutions they exert a great 
tendency to change to the trivalent form — Fe + + + and Mn + + + — 
hence on contact with the air, these mixtures turn dark and 
gradually form precipitates of Fe(OH).. and Mn(OH) 3 , respec- 
tively, because the change to the trivalent form is brought about 
by the oxygen of the air, according to the equation : — 
2Fe(OH) 2 -fO+H,0=2Fe(OH) 3 . 

Mg + + :— not affected by NH 4 C1+NH 4 0H. 

Bi + * + . Fe + + + . A1 + + + : — theso ions are precipitated completelv 
as hydroxides, Bi(OH) 3 , Fe(OH) 3 , A1(0H) 3 . 



- - * SCHOGH I INTRODUCTORY CHEMISTRY 



Ahravs hare a large quantitY of an ammonium salt in a solu- 

:-:-•-:. - :. T —:".-.-. tz - :: . -_. :.: - - :-> ^l:i :: !«:. 

-: ----- T i:-r :: :i* I:z I : ±e If-- :: 

The non-precipitation, bv XH 4 C1— XH 4 0H. or 
and Mn~ * has not been accounted for in Art. 10 and is to be eon- 

To understand the effect of ammonium chloride upon am- 
monia, we must recall Question 7 in the "Questions on Chapter 
VII." It is shown in the solution to this question that an in- 
crease in the concentration of the H~ ion (by the addition of 
HO) brings about a decrease in the concentration of the other 
ion— the acetion. 

A link >: lis: ieratios repeals -is: ill the stale m^nrs concern- 
ing acetic acid made in the solution to this question applj equally 
well to XH.OH. When Xfl 4 Cl is' added to a solution of am- 
monia, the number of XH 4 " ions per ex. is increased, and hence 
the number of OH" ions per ex. will be decreased bj the forma- 
tion of unionized XH 4 0H molecules, just as in the illustration 
with acetic acid, an increase in H~ ions brings about a decrease 

Since XH^Cl is largely ionized, while XH 4 0H is but slightly 
ionized, the XH/ ions added by means of XH # C1 amount to an 
enormous imcrease in XH 4 " ions in the solution, and hence bring 
about a correspondingly large decrease in OH" ions. This sires 
such a small concentration of OH" ions that such a solution would 
present — with the bivalent cationi . * and Mn* *■ — the 

:-'. -_ z ::. -. - : ■'.".■-:" _• rr: r. z — 

pir*ixroH-r<pig**]x[OH-]» 

Contents in water 

mixture of 1 _ lit, saturated from solid 

with XH 4 CL and XH^OH. Mg(0H) 2 in it 

Hence the combining tendencr of the ions in the mixture on the 

leftistoosniantoproduceapplLof Mgr(OHjL- But with tnvalent 

- :: - -v. ::. i> -_! r- - " :' :-- :- -.- : -'. r.l-= - r-. 

rAh-]vroH-] 3 >rAi— ]x[OH-p 

:r.:.r"T« :z zzittiz^ .:„--:-- ::. :: z~:r- 

of £t*^ salt. XH.C1 saturated from soM 

ffldTi:: Al(OH) 2 init 

Ut~:^ :'-i zziTTir^ :z - ■ • :-:*= 



Chapter X 129 

To express, in a few words, this difference in the precipita- 
tion of these bivalent and trivalent metal hydroxides, we would 
say that the concentration of the OH - ion is too small for the 
precipitation of these bivalent, but large enough for the precipi- 
tation of all trivalent metal hydroxides. 

Note. — With Mg(OH)«, the concentration of the OH - ion 
has to be raised to the second power in expressing its effect upon 
the reacting tendency; with Al(OH) 3 , the concentration of the 
OH" ion has to be raised to the third power: the concentration 
must always be raised to the power expressed by the number of 
parts taking part in the reaction — which is 20H~ for Mg(0H) 2 
and 3 OH~ for Al(OH) 3 . This relation is one of the fundamen- 
tal facts in nature, and this whole relation between concentra- 
tion and reacting tendency is known as the Law of Mass Action. 

13. Illustration of the Action of Ammonia With and Without 

Ammonium Chloride with Solutions of Magnesium, of Fer- 
rous, or of Manganous Salts. 

Experiment. — Put into each of two test-tubes about 5 c.c. of a mag- 
nesium salt solution. To one test-tube, add a few drops of ammonia 
from the reagent bottle on the desk, and note that a precipitate is ob- 
tained. The reaction is metathetical : — write the equation. 

To the other sample of magnesium salt, add an equal volume of ammo- 
nium chloride solution from the reagent bottle on the desk. Close the 
test-tube with the thumb (or with a suitable rubber stopper which should 
be kept on hand for the purpose) and mix the solutions by shaking the 
test-tube lengthwise vigorously. Then add a few drops of ammonia to 
the mixture: no precipitate should be formed. If &ny precipitate is ob- 
tained, then more ammonium chloride is required. 

Repeat this trial with a sample of a manganous salt. The same re- 
sults should be obtained with this salt. 

14. Illustration of the Effects Produced by Ammonia on the Salts 

of the Common Metals. 

Experiment. — To become familiar with the results produced when am- 
monium chloride and ammonia are added to solutions of salts of the com- 
mon metals, secure twelve clean test-tubes, put them on the test-tube rack, 
and put into each one 2 c.c. of one of the solutions of the following salts: 

Ag + , Hg + Hg ++ , Cd ++ , Pb ++ , Fe + + + , Fe ++ , 

Cu ++ , Bi + + + , Al + + + , Mn ++ , Ca + + , 

Add to each one 2 c.c. of ammonium chloride solution. The solutions of 
Ag + , Pb + + , and Hg, + will give precipitates of the chlorides of these metals. 
A precipitate may also appear in the Bi + + + solution : such a precipitate 
is BiOCl, a oasic salt, formed on account of conditions which need not 
be considered here. To dissolve this precipitate add dilute hydrochloric 
acid, a few drops at a time, shake the mixture, and thus continue until 
the precipitate has been dissolved (changed to BiCl 3 by metathetical reac- 
tion :— BiOCl+2HCl=H 2 0+BiCl 3 ) . 

None of the other mixtures will undergo any changes. 

Next, add to each test-tube, in turn, a small amount (about 1 c.c. of 



130 Schoch: Introductory Chemistry 

ammonia and shake the mixture: — if the ammonia produces a precipitate 
or appears to dissolve a precipitate that is present, add more ammonia, 
shake the mixture again, and so continue until the further addition of 
ammonia produces no further effect, Xote the results and compare them 
with the foregoing list of results. 

15. Ammonia as a Means for Separating Cations. 

Experiment. — Secure about 10 c.c. of a solution containing bismuth 
and copper salts — or aluminium and nickel salts — or ferric and magnesium 
salts. Add to it ammonium chloride and ammonia in sufficient amount 
to precipitate the trivalent metal completely (how do you ascertain when 
just enough has been used?). Filter the mixture, transferring all the 
precipitate to the funnel. When all of the solution has drained off, fill 
the funnel full of distilled water; allow this to drain off completely, and 
again fill the funnel with water. Thus the precipitate is "washed" clean 
of any adhering portions of the original solution. When the funnel has 
drained clean again, put another clean receiver under the funnel, drip 
some dilute hydrochloric acid upon the precipitate until it is dissolved. 
What does the new solution contain? Give equations for all reactions. 
This exercise illustrates the use of ammonia as a separating reagent. 

HYDROGEX SULPHIDE AS A REAGENT. 

Xote. — Hydrogen sulphide is poisonous, hence generators of 
this gas should be used either outside of the building or in hoods 
in which there is a' strong draft. 

16. Preliminary Consideration. 

Hydrogen sulphide is a weak acid : in its aqueous solution it 
is only slightly ionized into 2H + and S" ~. When the concentra- 
tion of the H + ion in an aqueous solution of hydrogen sulpiride 
is increased (e. g., by adding HC1). the concentration of the S" " 
ion becomes less for the same reasons for which the concentration 
of the OH" ion in ammonia becomes less when the concentration 
of the XH 4 + ion is increased. 

17. General Facts. 

The sulphides of the alkali metals and of the alkaline earth 
metals (Xa, K, XH 4 , Ca, Sr. Ba, Mg) are soluble in water: 
hence hydrogen sulphide does not react metathetically with solu- 
tions of salts of these metals. It does not react with salts of Al, 
because A1,S 3 is decomposed by water, according to the equation — 

Al 2 S 3 +6HOH=2Al(OH) 3 +3H 2 S. 

All other sulphides are insoluble; hence hydrogen sulphide re- 
acts metathetically with the neutral (or alkaline) solutions of 
salts of all metals except the above. With the twenty metal ions 
which we are considering in this chapter, the following precipi- 
tates would thus be obtained by inetathetical reaction: Ag 2 S, 
Hg 2 S, HgS ; CdS, PbS, CuS, Bi 3 *S„ Fe 2 S 3 , FeS, XiS, ZnS, MnS. 



Chapter X 131 

But when a solution contains free H + ion in moderate concen- 
tration (when as much of a strong acid such as HC1, H 2 S0 4 or 
HNO s has been added to it so as to give [H + ]r=0.2 to 0.27 grams 
per liter) then hydrogen sulphide precipitates only the following 
sulphides (by metathetical reaction) : Ag 2 S, Hg 2 S, HgS, PbS, 
CdS, CuS, and Bi 2 S 3 ; and it does not precipitate the ions Fe + + + , 
Zn + + , Fe + + and Mn + + . 

A solution of methyl violet may be used to determine the con- 
centration of H + ion here required. Put two or three drops of 
such a solution in a clean porcelain dish, add a slightly larger 
number of drops of the solution to be tested and mix the solu- 
tions : — a blue tint shows that the solution to be tested has a lesser 
concentration of H + ion than is here required, a blue-green tint 
indicates the proper concentration of H + ion, and a yellow-green 
(or yellow) tint indicates too great a concentration of H + ion.. 

The following table presents the colors of methyl violet corre- 
sponding to certain approximate concentrations of H + ion, which 
is included for reference only: 

Conct. of H + 1.000 1ST 0.100 N" 0.010 N" 0.001 N" 

Color of methyl violet yellow green blue violet 

Since the core of most "indelible" pencils (violet) contain 
methyl violet, streaks of such a pencil, made on white paper, may 
be used in place of the methyl violet solution above: it is merely 
necessary to moisten these streaks with the solution to be tested. 

Commit all the above general facts to memory. 

18. Explanation of the Difference Which H 2 S Shows in Its Effect 
When the H+ Ion Concentration is Large or Small, Respec- 
tively. 

The above difference in the effect produced by H 2 S depends 
upon the following two fundamental facts (a) and (b). See 
also Article 12, which explains similar relations for ammonia. 

(a) The concentration of the unionized H 2 S molecules is the 
same in all of its saturated solutions. Hence their ionizing tend- 
ency is the same in all solutions; and since the latter is equal to 
the combining tendency of the ions — that is, kX[H + ] 2| X[S~~], it 
follows that the value of the latter product is the same in all of 
these solutions saturated with H 2 S. Hence, when [H + ] has a 
large value (as in acidified solutions!) [S~~] must have a small 
value, and when [H + ] has a small value (as in neutral or alka- 
line solutions) [S"~] has a larger value than in acidified solu- 
tions. 

(b) The sulphides Ag 2 S, Hg 2 S, HgS, CuS, CdS, PbS, Bi 2 S 3 , 
which are precipitates even when the H + ion concentration is 
moderately large (as in acidified solutions), are less soluble than 



- :-:och: Ixteoducioey Chemistey 

those sulphides (ZnS. MnS, PeS, XiS) which are not precip- 
itable out of acidified solutions. 

Hence the former sulphides (CnS, aller amounts 

of unionized molecules in their saturated solutions (i. e., in mix- 
from which they hare been precipitated), and since the 
unionized molecules are in equilibrium with theix ions, it follows 
also that the ion-products of the former sulphides 
in mixtures from which they have been precipitated are smaller 
than the ion-products of the latter sulphides (ZnS, etc.) in mix- 
tures from which these have been precipitated. 

two facts — (a) and (b) — ^before a evident 

that in the introduction of H,S into anv solution containing sim- 
alts of A r -. Hg* H_--". Cu + * ( > ". P " -. :r Bi+ + * the 
products of the ions (e. g., [Cu" + ] X [S~ ~] ) in the original mis- 
will always — even in acidified solutions — be larger than the 
products of these ions in a solution saturated with the sulphide — 
hich is the resulting mixture. Hence, in the original 
mixture, the combining tendency of the ions is greater than their 
combining tendency ir. the solution after reaction when the com- 
bining tendency of the ions and the ionizing tendency of the 
unionized CuS are in equilibrium. Therefore the ions combine 
to form the precipitate of CuS. In symbols, this condition that 
brings about reaction is expressed thus : — 

[Cu-]X[S--]>[Cu-;JX[S--] 
in original in mixture after 

mixture before reaction — i. e., in 
reaction. a solution saturated 

wi: 

But with salts of Zn**, Mn " ~. 2 v ~:~ ~. F , and Fe", this 
relation exists only when [S~ "] is rather large, which is the case 
only in the absence of H* ions. 

The following numerical values obtained from actual measure- 
ments present- a relations in a definite manner: 

(a) Plain water saturated with H 2 S contains (1/10) 15 gram- 
ions of S" " per liter. 

(b) Acidified water (i. e^ N 10 H :urated with H,S 
contains ( 1 1 ) 21 S~ " per li - 

(c) Plain water saturated with zinc sulphide contains 
(I/O)'- 5 gram-ions of Zn*~, and also of S __ , hence the ion 
product for this solution is (1/10) w . 

(d) Plain water saturated with copper sulphide contains 
(1/10) 21 gram-ions of Cn* + , and also of S"". hence the ion 
product for this solution is (1/10) 42 . 

(e) If a plain solution of an ordinary zinc salt containing 
(1/10) gram-ion of Zn* * per liter were saturated with H 2 S, and 
any possible precipitation were delayed temporarily, then the solu- 



Chapter X 133 

tion would contain enough Zn + + and S" " to give an ion product 
of (1/10) (1/10) 15 or (1/10) 16 ; and this would be greater than 
the ion-product of a saturated solution of zinc sulphide (see c) ; 
hence zinc sulphide would be precipitated from this solution. 

Similarly, if a plain solution of an ordinary copper salt con- 
taining (1/10) gram-ion of Cu + + were saturated with H 2 S, and 
any possible precipitation were to be delayed temporarily, then 
the solution would contain enough Cu + + and S~ ~ ions to give 
an ion-product of (1/10) 16 ; and this would be greater than the 
ion-product of a saturated solution of copper sulphide (see d) ; 
hence copper sulphide would be precipitated from this solution. 

(f) But if, instead of plain solutions, acidified solutions of 
these zinc and copper salts, respectively, are employed, then the 
S~" concentration produced by saturating them with H 2 S would 
be only (1/10) 21 : and the product of the Zn + + (or Cu + " + ) times 
the S~~ concentration would be (1/10) 22 : for zinc, this last value 
is smaller than the ion-product of ZnS in a saturated solution of 
zinc sulphide, and hence no precipitation will take place; while, 
for copper, this last value still is larger than the ion-product of 
CuS in a saturated solution of copper sulphide, and hence precip- 
itation will take place even with this acidified solution of copper 
salt. 

Solutions of ordinary salts of Ag + , Hg + , Hg ++ , Cd ++ , Pb ++ , 
and Bi + + + behave like the Cu ++ solution above; while solutions 
of ordinary salts of Mn ++ , Fe ++ , Fe + + + , and M + + behave like 
the Zn + + solution above. 

19. Colors of Precipitated Sulphides. 

The colors of sulphides are a valuable means of identifying the 
metals. Freshly precipitated sulphides have the following colors: 

FeS, MS, Ag 2 S, HgS, PbS, Bi 2 S 3 — dull black. 

CuS — Brownish black. 

ZnS — white (when pure!) 

CdS— yellow. 

MnS — pink or flesh color. 

Note, — During precipitation, HgS frequently exhibits several 
other colors — black, yellow, red — but with excess of H 2 S it finally 
becomes black. 

20. Beagents Which Act Upon Sulphides and Produce Soluble 

Compounds of Their Metals. 

(a) Dilute HC1 or dilute H 2 S0 4 react metatketically with the 
following: ZnS, FeS, Fe,S 3 , MnS, CdS. (CdS requires a more 
concentrated "dilute" acid than the others.) 

(b) HN0 3 , dilute or concentrated, acts upon all the sulphides 



:,-. :-V- :t ■: it :ztt:: :t: 



"IT ' 



L LTT. : LL'l- _T LIT. : 1. .TOT 





.:":-" :v 



Tl.r _T TT- .L~ T~- T14 

H„£ feir -oQBcte ^rrnVi ^rte j— ii* fan ikb£ urarik & Iw 

: :-:_ .z_tl :_ til ftttt_:- >~Z. - lit tt-t -.:-_..:---? ttt- 
~li - --i - H--.-T-"- .-l_- vttl lt- ;;..-.; _i- - J-" Mjit- 



L I :*T.L 7'-' ~ L TrTt 




Chapter X 135 

Art. 17. The mixture contains about 1.5 gram-mols. HC1 per liter, and 
with approximately 60% of this HC1 in the form of ions, the mixture con- 
tains 1.5 X. 60—0.9 grams H> ion per liter. This concentration of H + 
ion is too great to permit the precipitation of CdS even, as will be shown 
by the following trial: 

Put the mixture into a flask (preferably an Erlenmeyer flask of about 
300 c.c. capacity) which has been fitted with a one-hole rubber stopper 
(No. 5) and a short piece of narrow glass tubing which extends about 
half-way to the bottom of the flask and which terminates in a fine open- 
ing ( nozzle ) . This end should not extend into the liquid ( see foot note ) . 

With the stopper resting loosely on top of the flask, let the H 2 S gas 
flow into the flask until most of the air in the flask has been displaced by 
H 2 S. Then fit the stopper into the neck, and shake the flask vigorously 
to bring the liquid into intimate contact with the H 2 S gas and thus 
hasten the saturation of the liquid with this gas. If the acid used was 
not too dilute, no precipitate will appear in the liquid. 

Next, add 50 to 60 c.c. of distilled water, and saturate the mixture 
again with H 2 S as before: a copious precipitate of CdS should have been 
formed. If not, add another 50 c.c. of water. Test, with methyl violet, 
the particular solution in which extensive precipitation takes place: — the 
indicator-mixture should give a blue-green color. 

Now secure 5 c.c. of a zinc salt solution, add only 5 c.c. of dilute HC1, 
add 100 c.c. of water (twice as much as was used with cadmium), put the 
mixture in a 300 c.c. Erlenmeyer flask and saturate it with H 2 S: no pre- 
cipitate should appear. Add another 50 c.c. of water, and treat again 
with H 2 S: — still no precipitate should be formed. 

Next, add about 10 c.c. of ammonia solution from the reagent bottle on 
the desk. This solution contains about 4 gram-ions per liter and 5 c.c. 
of it is enough to neutralize the acid in the mixture. Saturate the mix* 
ture with H 2 S again and shake it:— a white precipitate of ZnS will be 
formed. 

Bead Article 17 again carefully, and note that this experiment 
demonstrates the facts therein presented. 

23. An Illustration of the Use of Hydrogen Sulphide as a Reagent 
for Separating Certain Metal Ions. 

Experiment. — Secure 10 c.c. of a solution of a mercuric salt and 10 
c.c. of a solution of a nickel salt, add about 3 c.c. of dilute HC1, mix them 
in a 300 c.c. Erlenmeyer flask, test the mixture with methyl violet (see 
Art. 17), and add either water or dilute HC1 as may be necessary to 
secure the H + ion concentration which will allow all of the mercuric ion 
to be precipitated, but which will prevent the nickel ion from being pre- 
cipitated. Then treat the cool mixture with H 2 S gas as directed in the 
preceding experiment. Fit a filter paper carefully into a funnel, and hang 
the funnel on a wooden funnel stand in such a position that its stem will 
extend into a beaker placed underneath to receive the filtrate. The stem 
should touch the side of the beaker so that the filtrate will run down the 
side of the beaker instead of "splashing" down. Being careful in such 

Foot Note. — For convenience in class use, all students should be sup- 
plied with flasks which will fit the same sized stopper. The stopper and 
glass tube should be fastened in the hydrogen sulphide supply pipe. As 
long as the glass tube does not extend into the liquid, and terminates in 
a small opening, it will remain clean on the inside, and hence to clean it, 
as well as the stopper for the next time it is to be used, they need only 
to be wiped clean with a towel, or to be rinsed with a stream of water 
from a wash bottle. 



136 soch: Ixteoductoet Chemistey 

manipulations is essential to success in this work! Filter the above 
mixture, using a stirring rod in pouring, as shown in the figr i 
which should be io<: -.re fully. Wash the precipitate" twice with 

water as directed in Art. 15. and collect the wash-water with the filtrate. 

A new precipitate may be formed when the wash water dilute - 
filtrates. — but whether it does or not. test the acidity of the filtered 
liquid, dilute it if necessary, and treat it again with H ; S to make ta 
that all of the mercuric ion has been precipitated: should more E_ - 
thus obtained, filter the solution through the 3ame filter paper, and wash 
the latter again tieice, — but throw these washings a- 

To dissolve the mercuric sulphide: If the amount of precipitate on the 
filter is large enough, take it up with a small porcelain spoon and put 
it into a small clean porcelain dish. If ther -ough precipitate to 

handle it that way. open the filter paper ill the paper parts which 

are not covered with precipitate, and put the paper with the precipitate 
on it into the dish. Cover the materi.- sh with a small amount 

of ordinary dilute nitric acid, and warm the mixture. The precipitate 
may turn white or "cream"' color, but a careful inspection will show that 
A dissolved. See £ : that nitric acid should 

not attack H28. Decant the liquid carefully, add a little water and 
decant again, throwing these liquids away as useless. Now put upon the 
material in the dish a small amount of concentrated HC1, warm the mix- 
ture, and add. gradually, several small crystals of potassium chlorate. 
When the precipitate has been acted upon, remove the floating lump of 
sulphur land also the filter paper :1 it for a minute 

expel the chlorine. Then pour the solution into a labeled test-tube for 
later use. For an explanation of the reaction in this mixtur 

To the filtrate above from the precipitate of the HgS, add on- 
its volume of XH 4 C1 solution, and then just enough ammonia so that, 

after thorough stirring, the mixture will emit the odor of free ammonia. 
This assures you that all of the free acid has been neutralized. Then add 
10 c.c. of ammonium sulphide solution, stir the mixture, and fih 
To make certain that you have used enough ta precipitate all of 

the Ni* " ion. add a few drops more to the filt- 
is thus obtained, add several c.c. of ' XH t & to the filtrate and CM 
through the same funnel. Again test as above to ascertain if pre 
tion is complete. When precipitation is complete, wash the - 
on the filter twice with : Then put another receiver under 

the funnel and pour upon the precipitate on the filter some dilute H — 
assure yourself from Art. 20 that this should produce no change. Wash 
off this" acid with a little water, then the precipitate to a dish 

as you transferred the HgS above, cover it with concentrated HC1. add a 
few" drops of concentrated HXO. and warm the mixture: note from the 
color that a solubl- R H has been formed again via! is formed?; 
and then throw this material away. 

Put into a separate test-tube a little of the mercuric chloride solution 
prepared above, and add to this an equal amount of stannous chloride 
solution: — a white precipitate (HgXV or a gr- Big will 

be formed according to one of the following equati 

2HgCL-- : =--::-"- 

HgCL- BeCfc=Sa€ I . - B g 

This behavior is characteristic of mercuric salts. 

Put into your note book a brief account of all that has hap- 
pened in this procedure, and give all equations. 



Chapter X 137 



24. Exercise. 



The answers to the following questions are to be carefully ar- 
rived at, then written out, submitted to the instructor, and after 
they have been passed upon by him, they are to be carefully im- 
pressed upon your memory. 

The • following questions refer to the mixture worked in the 
preceding experiment: 

1. If a. magnesium salt is also present in this mixture, what 
becomes of the Mg + + ion during the course of the procedure ? 

2. If silver salts are also present in the above mixture, what 
would happen at the beginning of the procedure? What would 
be the best method to remove the Ag + ion so that it would not 
interfere with the rest of the procedure as given? 

3. If aluminium salts are also present in this mixture, what 
would happen to the Al + + + ion in the course of the procedure ? 

4. What other metal ions, if present, would have shown the 
same behavior as the Ag + ion in Question 2 above? 

5. What other metal ions, if present, would have shown the 
same behavior as the mercuric ion in the experiment above ? 

6. What other metal ions would have shown the same behavior 
as Al + + + in Question 3 above? 

7. What other metal ions would have shown the same behavior 
as magnesium in Question 1 above? 

25. The Formation of Free Sulphur From Hydrogen Sulphide by 
"Oxidizing Agents." 

Solutions of certain substances act upon H 2 S in such a man- 
ner as to change the S - _ ion to S° — i. e., sulphur — and when 
this takes place in dilute solutions, the sulphur remains finely 
divided and the liquid has a white, "milky" or turbid appearance. 

Experiment. — (a) Put a few c.c. of a solution of ferric chloride into 
a test-tube, add a few drops of dilute HC1, and several c.c. of H 2 S water. 
Note the appearance of the liquid. Heat the solution to its boiling point 
for several minutes: most of the sulphur will collect into a few globules 
which will float on top of the liquid. The reaction in this mixture is 
expressed by the equation: — 

2FeCl 3 +H 2 S=2Fe.CL+2HCl+S 

The theoretical view of this change will be given in a later chapter. 

(b) Put a few c.c. of ordinary dilute HNO., into a test-tube, heat the 
liquid, and add 2 to 3 c.c. of H 2 S water. Note the appearance of the 
liquid, and the presence of free sulphur in it. The following equation 
expresses the reaction in this mixture: — 

3H 2 S+2HNO s =3S+4H 2 0-l-2NO 

This formation of free sulphur from H 2 S is frequently en- 
countered, and the student should be familiar with the "white" 
appearance of the resulting solution. This change is also effected 
by the oxygen of the air, 



13S Schoch: Introductory Chemistry 

H 2 S-J-0=H 2 0-hS 

and it is likely that the sulphur deposits in the earth which 
furnish us sulphur have been produced from ELS, which orig- 
inated far down in the earth and which was oxidized when it 
came in contact with air. 

26. The Separation of the Common Metals Into Five Groups for 
Qualitative Analysis. 

The experiment and the exercise just preceding show the stu- 
dent how these reagents may be used to separate metal ions 
(cations) and to recognize them by the formation or non-forma- 
tion of certain compounds. The determination, by such means, 
of the metal ions and acid ions (anions)* present in various salts, 
acids, and bases is called QUALITATIVE ANALYSIS. How- 
ever, in the attempt to identify an unknown substance, use is 
made not only of the facts concerning the general reagents NaOH, 
XH 4 OH, and H_,S, but also of the facts of solubility learned in 
Chapter VI and of special reactions peculiar to individual ele- 
ments. With the aid of all the facts at our command, the search 
for and identification of the constituents of a salt, acid, or base 
would still be quite complex were it not for the organization of 
these facts. The general survey of the facts leads us to group 
the common metal ions into five main groups. This enables us. 
when working with an unknown mixture, to separate the metal 
ions into at ] . groupings, if necessary: the task of iden- 

tifying the constituents of each of the five groups becomes, then, 
a matter of less difficulty. 

The five groups in our qualitative analysts, together with the 
metal ions which comprise each group, are: 

1. Insoluble Chloride Group. 

AgCl. HgXL. PbCL. 

2. Acid Sulphide Group. 

HgS. PbS. B - >. CdS. 

3. Ammonium Sulphide Group. 

Al(OB - . F • >. XiS. MnS. ZnS. 

4. All-aline Earth Group. 

BaC0 3 . CaCO :; , SrCO,. MgC0 3 . 

5. All-ali Group. 

Xa-. K-. NH 4 + . 

Only tests for simple anions will be made in this course. The 
anions which will be tested for are CO a " Ac", CI", S0 4 ~- KOf, 

and PC. . The directions for these tests are to be found in 

Art. 39/ 



Chapter X 139 

The procedure which will be pursued in the work to follow is: 

(1) To identify and confirm the members of the first group 
in solution singly as knowns. Anions are also to be determined. 

(2) To separate, identify, and confirm the members of the 
first group in a mixture as knowns. Anions are also to be deter- 
mined. 

(3) To separate, identify, and confirm the members of the 
first group, singly or in mixtures, as unknowns. Anions are also 
to be determined. 

(4) Each succeeding group will be tested just as the first 
group, solutions being used solely. 

(5) After a complete survey of the field has been made by 
working with known and unknown acids, bases, and salts in solu- 
tion, unknowns consisting of solids will be handed out for iden- 
tification and separation. It is desired that the student should 
become familiar with the appearance and chemical behavior of 
special salts, oxides, and minerals. The student will be required 
to note in his note book all the facts of appearance and behavior 
peculiar to his particular unknown. 

Mixtures may contain two or three different cations or anions, but care 
will be taken to avoid using or forming solids which are insoluble in 
acids or aqua regia (i. e., AgCl, PbS0 4 , BaS0 4 , SrS0 4 , CaS0 4 . and sili- 
cates). Phosphates of the third and fourth groups will be avoided and 
only those of the alkalies and of the first and second groups will be 
given out because the scheme below does not take care of others. 
Among these compounds will be included: — iron sulphide; iron pyrites 
or "fool's gold"; quicklime; manganese dioxide or pyrolusite; sodium 
phosphate; copper phosphate; red oxide of mercury; mercuric sulphide 
or cinnabar; lead sulphide or galena; zinc sulphide or sphalerite; ferric 
oxide or haematite; ferrous sulphate or copperas; ferrous ammonium 
sulphate or Mohr's salt; ammonia iron alum; potash alum; sodium car- 
bonate or "washing" soda; sodium bicarbonate or "cooking" soda; mag- 
nesium sulphate or Epsom salts; sheet lead; commercial silver or Mexi- 
can silver coin; nickel coin; Monel metal (a nickel-copper alloy) ; and 
the coatings on galvanized iron or roofing tin. 

27. Beginning of the Procedure for the Qualitative Analysis of 
Certain Compounds of the Common Metals with Some Gen- 
eral Directions of Manipulation. 

Make a heading in your note book designating and describing 
the substance which has been handed you to be analyzed. 

The substance handed you may be in solid form (soluble in 
water or in acids) or in solution. The procedure to be followed is : 

(1) Solutions are to be subjected at once to the regular pro- 
cedure of the qualitative analysis scheme beginning with Art. 28. 
Only a portion (about one-third) of the sample given you should 
be used: reserve the remainder for "repeats" and the anion tests, 

(2) Non-Metallic Solids should be powdered or crushed finely 
in a mortar. Put a "pinch" of it in a clean test-tube, add 5 c.c. 
of water, heat the mixture to boiling, and note if the solid is 



'--'. -rr "::::■■:::-.". zz::>rzv 



•.:I~: !•= :_ ~:^r I: .: :.= =.:.-:lr :~ -i:-:. L^:>r i lirrrj :•;:- 
ticn (not ill!) and proceed iriin the regular procedure as in (1). 

H 
r:/:Z t-;-_z:^ ; :..-,lt::.--\ ZZ I:i: :':: mrnrr i: -.::.■= 
if ifti-:- If like solid does not dissolve appreciably, 

try another pinch similarly in concentrated EXO,. If it dissolves 
:l :-:.::: 7 :: :'. .- i::i« :7.:l,. i:i i _-lr :•;-_ :,!:::.- : . Z 71 
:: ::.:- :-:-:: -^ •:-:.:.::: ::_- F\" ; :ii: -I -,— : :lr 
>:Z " =*: :"" Lsf >■= :. ::.: = zmriTT. '-.iz^ :z- ft:::.:: — :77 r.:: 
":•► Z-.l>" l =•:" : ~7::ii — Z i;: Z?=-:>f :: :r.r :: :::i: ~r:7:i 

haierer mo: eeessary to emptor. Toe greater por- 

■ - - 
":■-.'. t>:t:-Z::l Zf": -ji: 7:?Z.Z : -;:- :::-•:. Jrx-rZ — :: 
die efaor solution as in (1). Hake a note book entry of all the 

: ._- •:: :- ^:":jr: :: ::?- :>•: "Z: =•:!::! 

.- . : . - - ". . . 

_ 
-ill recall (a) that all aridt* of metals react with 
- " 
jA (c) all carbonates and pkospkales are disrobed by 

— :": ?T-:r.r i: " c 



:: : :•::.--. r:Z :: - -:ZZ -■-•;:.----;. :Z ::it:«:^: :::: Trzzizzi 
:: ?•:"_--'::. Z:: : i • •- - " - "- --::■-: zz . ":: t':.-z. lz zz^'zz- 
:'.r ::j?::i^ r.: Z .\= Z.. J . .. : = i::Z -::•:: -7 s ??:-::r i:Z 
-*rZ :::::•" - • ZZ- "Z=-\:--:- -"■ . -- : - : :: : ■ ■- z-zzzLzi 

Ca,(P0 4 ) 2 -f4HO=2CaCL-fCa(aP0 # ) a 
The primary ealehnn acid phosphate, Ca(H.PO # ) ». ionize* ei- 

■:z- 

ions, and (H = P0 4 )~ ions, with a cer- 

T.iir. ~z:~.<:zz::z :z i_ ::- Toff::.: :•::: :zi~. l ; i~ ":::.::^: Tor- 
tious. When a base (e. g^ annnonia) is added to soda a nrixtore. 
the c zrrerted to a normal salt: the soluble 

-■:-7.::-iz: :::: "1 -;_:.:- :"= i-::-:^: :::: ti-e ::--:""*: 

: : - ; : t z : ,c - .' - " " - — 

:::. -.: :: -::~z. :z= : - ?:. ,-:;z.::- 



Chapter X • 141 

solved, evaporate most of the acid b} r gentle heating (on an as- 
bestos board high above the flame). If an insoluble powder has 
been formed by the action of the acid, decant the liquid from it 
or remove by filtration, and proceed with part of the clear liquid 
as in (1). 

State in your note book whether or not the metal changed en- 
tirely to soluble compounds. 

An insoluble powder formed during the entire acid treatment 
is either antimony or tin oxide, but these are not to be considered 
in this analytical work, and hence such residues may be thrown 
away. 

28. Determination of the Cations — Group I: Metals Whose Chlo- 
rides Are Insoluble. 

A solution of any compounds soluble in water or nitric acid 
may contain Ag + , Hg + , Pb + + , — hence when enough of a chloride 
is added to such a solution, these cations will be completely pre- * 
cipitated (except the slight amount of Pb + + which corresponds 
to the perceptible solubility of PbCl 2 ). 

Preliminary Trial to Ascertain if Any of These Metals Are 
Present. — Put 1 c.c. of a solution that could contain ( f ) these 
cations in a test-tube, add ten drops of dilute HC1 and shake 
the mixture. A permanent (see Note below) precipitate shows 
that one or more of the cations of this group are present, and 
they should be precipitated out of a large amount of sample as 
directed below. In the absence of a precipitate, nothing further 
in this article nor in Art. 29 applies to this solution, and the 
next trials with it are to be made according to Art. 30. In any 
case, the. mixture made in this preliminary trial will not be 
needed further. 

Note. — If the solution contains salts of bismuth, then a white 
precipitate of BiOCl is frequently formed when the first por- 
tions of HC1 are added to the solution; but this precipitate re- 
dissolves when enough dilute HC1 is added. 

Complete Precipitation of Group I Out of the Main Sample. — 
Take 10 or 15 c.c. of the main solution prepared according to 
Art. 27 (prepared in this way either by the student, or by the in- 
structor), put it into a small or medium size beaker, and add 3 to 5 
c.c. of dilute HC1, stir the mixture, allow the precipitate to settle, 
then add a drop or two more of HC1 to a clear part of the liquid 
and note whether or not more of the precipitate is formed: — if 
more is formed, add } c.c. more of HCi, stir again, test again to 
ascertain if enough has been added, and so continue until all of 
the precipitable cations have been precipitated by means of the 
least amount of HCI. Filter (see figure, Art. 5) and transfer 
all of the precipitate to the 'filter. Wash the precipitate twice 



142 



Schoch: IxiBODr: :: hxilistey 



with distilled water (for details of w Put 

the collected filtrate and washing? into i Rrks 

flask, cork it and lab-7 
aside for later use. 



29. Identification of the Cations in the Group I Precipitate, 

I fa small porcelain spoon, take a small porti: 

the precipitate from the filter above and pnt it into a small 
beaker, add water, heat the mixture to boiling, and £ : ugh 

a clean fifi if the amount of precipi: - small, pour hot 

upon the filter on which the pr 
collected. Add a drop or two of dil \ to th 

hot liquid. If a | obtained :ned from 

the PbCL by metathetical readier /blonde is 

much more soluble in hot water than in cold. 

If the "Group precipita: >e completely in hot 

water, then E_ 7 leode 

if the residue is composed of th— at a clean re- 

r under the last funnel used, and pour ammonia, dr 
drop, upon the precipitate on the filter. If the substance on the 

turns M we been present 

is pr i in the ammonia: add an acid (dilute 

HXO,) to the filtrate until all of the ammonia is neutralized, 
and :: . . .1 appear as a precipi: * 7 

explanation of ihese char_ 10. 

In order to sh reg :ing procedure at a gla: 

nted here again in outline form, 
on the filter:— A _ 

i : : • - z 



Filtrate: solution of PbClj; add dfl. H r SO« 
Ppt. PbS0 4 (wt: 



" " - " - - - — 
add. or shake op witJi ammoaia. 



Filtrate: acklifv 
arHh dfl. HXO, 
Ppt. AgCL 



unc nd 29. 



^ — - 






30. Determination of the Cations — Group H. 

rhis -roup includes all those sulphides which are precipitable 
from moderately acidified solutions except the cations of Group 
I. Hence, for the ration of this group, we solu- 

tion prepared according b AH from which the -: 

cations have been removed (see end of Art . : : r from which 
they are known to be absent — for instance, by the fact th&: the 



Chapter X 143 

original material was changed to soluble substances by means of 
HC1 or aqua regia. 

Preliminary Trial to Ascertain if Any of These Metals Are 
Present. — Put about 1 c.c. of the proper solution into a test-tube, 
add 5 drops of dilute HC1, and 2 c.c. of H 2 S water. If a pre- 
cipitate appears, any one or more of the cations Hg + + , Pb + + 
(small amount only!), Cd + + , Cu + + and Bi + + + are present, and 
they must be precipitated completely out of a larger amount of 
the sample as directed below. In the absence of a precipitate, 
nothing further need be done with the solution in this article 
and in Art. 31, and the next trials with it are to be made ac- 
cording to Art. 32. 

Complete Precipitation of Group II Out of the Main Sample. — 
Take 10-15 c.c. of the original solution prepared according to 
Art. 27 in which the cations of Group I are known to be absent, 
or take all of the filtrate from the precipitation of Group I (see 
end of Art. 28), put it into the 300 c.c. Erlenmeyer flask suitable 
for H 2 S gas precipitation (see Art. 22), add either dilute HCl or 
water until the H + ion concentration is correct (see Art. 17), 
treat with H 2 S gas as directed in Art. 22, and follow the direc- 
tion in Art. 23 with respect to testing for completeness in pre- 
cipitating, filtering, and washing the precipitate. The filtrate 
from which all of the Group II cations have been precipitated is 
then to be put into a suitable stoppered flask, labeled "Filtrate 
from Group" 11/' and to be set aside for later use. 

31. Identification of the Cations in the Group II Precipitate. 

Record the color (or colors, if several!) of the precipitate ob- 
tained with H 2 S, together with your inference, from these colors, 
as to the cations likelv to be present. This precipitate may con- 
tain HgS, PbS, Bi 2 S 3 , CdS, and CuS. The last four of these 
react with warm dilute nitric acid, but HgS does not. Hence, 
to separate the. HgS from the others, treat the mixture with 
dilute nitric acid — for details of operation, see Art. 22. If the 
precipitate is completely disintegrated, then HgS is absent, but if 
a residue remains,- Hg + + may be present. In either case, the dear 
liquid is to be put in a clean beaker or dish, 1 c.c. of cone. H 2 S0 4 
is to be added, and the liquid is to be evaporated as far as possi- 
ble on a large beaker full of boiling water (a water bath), or some 
corresponding heating apparatus. 

If a residue that might be HgS has been left by the nitric 
acid treatment, it should be treated as in Art. 22, while the pre- 
ceding evaporation is under way: — this procedure will show 
whether or not Hg + + is in the sample under consideration. 

To the residue (small bulk!) from the nitric acid evapora- 



144 . - sogh: Ixtboductoby Chemistey 

tion above, add a little water, stir the mixture, and try to r 
tain whether or not a small amount of white powder — i PbSOJ — 
is present: — This reveals itself if the vessel is given a circular 
motion so that the liquid rotates in the vessel. Of cours 
lead has been recognized in the first group of cations, it need 
not be recognized again here. In some samples, however, the 
quantity of lead is too small to give a precipitate of PbCL, hence 
>uld be looked for here. 
The next step in the search of the other cations that might be 
present in this soJutv is the addition of 

s ( ?) of ammonia to the whole sample under consideration. 
In the presence of an excess of ammonia, Cu" + and Cd" * form 
soluble compounds, but Bi is precipitated as Bi(OH) 3 . This 
precipitate should be white. If Cu* * is present, the solution 
will be deep blue. Collect the , on a filter, but keep the 

filtrate for further use as directed below. "Wash the Bi(0H) 3 
precipitate, then drip dilute HC1 upon it, and let the resulting 
drops of solution fall into a larsre beaker of distilled water. The 
HC1 changes the Bi(OH), to BiCl as long as the concentration 
of the H" ion is great ; but when, by dilution with water, the H" 
ion concentration is made very small, the reverse change takes 
place, — namely. H 2 and the salt Bid, react to form HC1 and 
the basic salt BiOCl, as per following equation: 

BiCL-H 2 C±^EiOCl-2Hei. 

Of all the common metal ions here considered, Bi is the 
only one that has this property. This reaction is known as 
hydrolysis: it is the reverse of the reaction between an acid and 
a base. All salts of weak acids or of weak bases undergo slight 
hydrolysis when they are dissolved in water. 

TTe must now return to the liquid in which Cd" + and Co.* * 
may be contained — i. e.. the liquid to which an excess of am- 
monia had been added and which may have been filtered to re- 
move a precipitate of Bi(OH) . If this solution is coloi 
then it is free from Cu** and it may be tested immediately for 
Cd ++ by means of ELS water (yellow ppt.. OdS). If the solu- 
tion is blue, secure a freshly prepared solution of potassium 
cyanide (care ! poison ! do not on your hands or breathe 

its fumes I, and while stirrinsr or shaking the mixture, add — drop 
by drop — the least amount of potassium cyanide with which the 
blue color will disappear. Then add H_S water. 

A yellow precipitate CdS shows the presence of Cd~ *". 

The potassium cyanide reacts with Cd~ ' salts as follow! 

First. Cd(CX) 2 is formed by metathesis — 

CdCl,--?KCX=Cd(CX) 2 -2KCl. 

Second. Cd(CX), unites with 2KCN to form a double cyanide, 
(KCX) 2 Cd(CX) 2 . 



Chapter X 



145 



To show the main ions of this resulting double cyanide of 
potassium and cadmium, its formula is written thus: — 
K 2 Cd(CN) 4 . It ionizes primarily into 2K + and an anion com- 
posed of Cd(CN)r". The latter ionizes further, — into Cd + + and 
4CN". This takes place only to a slight extent, yet sufficiently 
so that a precipitate of CdS is formed when H 2 S is added. 

The potassium cyanide reacts with Cu + + as follows : 

First, Cu(CN) 2 is formed by metathesis — 

CuCl 2 +2KClS T =Cu(CN) 2 +2KCL 

Second, the cupric cyanide dissociates into cuprous cyanide and 
free cyanogen — 

2Cu(ClSr) 2 =2CuCN+(CN) 2 . 

Third, cuprous cyanide unites with 3KCN to form the double 
cyanide K s Cu(CN) 4 . The secondary ionization of the latter, 
which gives Cu + + ions, does not take place sufficiently so that 
CuS may be formed when H 2 S is added (difference from Cd + + !). 

Make note book entries of the results obtained according to 
Arts. 30 and 31. 

The following table presents the following directions in out- 
line : 

Sulphides precipitated from slightly acidified solutions by H 2 S : 
HgS, PbS, BLS 3 , CuS, CdS; 

boil with dil. HN0 3 . 



Residue: HgS — treat with 
conc.HCl and add a little 
KC10 3 , boil off excess of 
chlorine, dilute with 
water and add SnCl,. 



Ppt. gray, Hg: 

white, HgCl. 



Solution: Pb (NO,),, Bi (NO,),, Cu (NO,),, Cd (NO,),; 
add a little cone. H 2 S0 4 and evaporate to small bulk — 
add H,0. 



Ppt. PbS0 4 . I Filtrate: salts of Bi, Cu, and Cd: add 
I NHjOH to slight excess. 
Deep blue color indicates copper. 



Ppt. Bi (OH), 

Dissolve by dropping 
HO upon the ppt. 
on the funnel and 
allow solution to 
run into a large vol- 
ume of water — ppt. 
BiOCl. 



Filtrate: salts of Cu 
and Cd. 

Add KCN drop by 
drop till solution is 
colorless — then 
add H,S,— ppt. 
CdS, yellow. 



32. Determination of the Cations — Group III. 

This group includes all the metals precipitated out of a solu- 
tion prepared according to Art. 27 when (1) the solution is ren- 
dered alkaline with ammonia (plus NH 4 C1) and when (2) 
(NH) 2 S is then added to the mixture, provided that the cations 
of Group I and of Group II are either known to be absent or have 
been removed. The precipitate thus obtainable may consist- of: — 
Al(OH) 3 , Fe(OH) 3 , Fe 2 S 3 , MS, FeS, MnS, and ZnS. 

Preliminary Trial to Ascertain the Presence or Absence of 
Cations of Group III. — Put into a test-tube about 2 c,c. of the 



146 Schoch: Introductory Chemistry 

original solution prepared according to Art. 27 if Groups I and 
II are known to be absent, or of the filtrate obtained after re- 
moving them completely (see last part of Art. 30 or of 28, re- 
spectively) ; add 1 c.c. of IMTI 4 C1 solution, 1 c.c. of ammonia, 
and a few drops of ammonium sulphide solution, shake the mix- 
ture vigorously, and note whether or not a precipitate is formed. 
Note the appearance of the precipitate, and infer from it what 
cations may be present: — enter your inference in the note book. 

Precipitation of Group III. — Secure the main portion of the 
solution of which a part has just been tested, add NH 4 C1 solu- 
tion to it to the extent of one-fourth (or more?) of the volume 
of the- sample, then add ammonia to it in small portions until, 
after shaking, the mixture turns red litmus blue, and then, if 
necessary ( ?), add ammonium sulphide solution in very small 
portions until after shaking, the further addition of a small 
amount of ammonium sulphide produces no further precipitate. 
Filter the mixture carefully, transferring all of the precipitate 
to the filter paper, and collecting the filtrate in a clean flask. 
Close this with a stopper, label it: "Solution for Art. 34," and 
set it aside. Immediately after the solution has drained com- 
pletely out of the funnel, fill the filter with water to wash the 
precipitate, but do not keep the washings — i. e., do not add them 
to filtrate from the original solution. When the filter has drained 
empty again, fill it again with water to wash the precipitate a 
second time. It may then be considered that the dissolved ma- 
terial in the original mixture has been washed out of the pre- 
cipitate. Proceed immediately to treat the precipitate as per fol- 
lowing paragraph. 

33. The Identification of the Cations in the Group III Precipitate. 

Put a clean receiver (beaker or flask) under the funnel which 
holds the Group III precipitate, and pour dilute HC1 drop by 
drop upon the precipitate on the filter, or if the quantity of pre- 
cipitate is large, remove a portion with a small porcelain spoon, 
put it into a small beaker, add 2-5 c.c. of dilute HC1, stir the 
mixture thoroughly, and if an insoluble portion remains, filter 
the mixture through a clean filter. All of the substances possibly 
present except NiS will dissolve in the HC1. Test the residue on 
the filter according to the second paragraph below. Put five 
drops of dilute HNO c into the clear solution just obtained, pour 
it into a small dish, place this on a "water bath" and allow the 
liquid to evaporate. 

In the meanwhile, proceed to test the residue on the filter 
above to ascertain if it is really a compound of M + + . Secure 
a piece of platinum wire, clean the end carefully, bend it into 
a circular loop of about -|-inch diameter, heat it to incandescence 



Chaptek X 147 

in the flame, dip it, while hot, into some powdered sodium meta- 
phosphate (NaP0 3 ) or into some microcosmic salt, and hold the 
mass in the center of the upper third of a Bunsen flame (the 
hottest -part). The salt should melt and form a clear colorless 
drop in the loop of the wire. If necessary, pick up more of the 
salt with the heated end, but do not attempt to make too large 
a "bead" because it drops off too easily when hot. Next, bring 
the hot bead in contact with some of the residue on the filter, 
and heat the bead again until it fuses. Care must be taken not 
to pick up so much of the solid as to make the bead opaque 
after it is fused again. If the latter has happened, the bead 
should be removed by fusing it and "throwing" it away, and a 
new bead should be made. If the amount of residue on the 
filter is very slight, tear off a small piece of the paper with the 
residue on it, stick it to the bead and put the whole mass in the 
flame. The components of the paper form nothing but C0 2 and 
H 2 on combustion, and hence nothing is left in the bead except 
the "residue." With a suitable amount of Ni compound, the 
bead will be transparent with a reddish brown color. In order 
to become familiar with the color due to nickel, a bead should 
be made with a Jcrwtvn nickel salt. 

In the meanwhile, the solution on the water bath will have 
been evaporated to dryness. Dissolve the residue in a very small 
amount of water (2.5 c.c), pour the solution into a test-tube, 
and add 5 c.c. of sodium hydroxide solution from the reagent 
bottle on the desk. Stir the mixture vigorously, and if it is 
"thick" with precipitate, add a little water plus an equal amount 
of sodium hydroxide solution to thin it. If a precipitate (not 
merely a "cloudiness") is present, filter the mixture: if the filter 
paper is attacked by the solution, dilute it to double its volume 
with water. Divide the liquid into two parts: to one part add 
an equal volume of ]STH 4 C1 solution ; and stir the mixture : — 
if Al + + + is in the sample under consideration, Al(OH) 3 should 
be obtained here. To the other part of the solution, add some 
H 2 S water: if Zn ++ is in the sample, white ZnS should be ob- 
tained here. If a precipitate has been removed above from this 
liquid by filtration, and it has a red or brown color, transfer a 
very little bit of it with a spoon to a dish, put a few drops of 
dilute HC1 on it to dissolve it, and add a few drops of potassium 
ferrocyanide : — if a deep-Hue color is formed in the mixture, iron 
is present in the sample. Take another small portion of the pre- 
cipitate on the last filter (or a bit of the filter with the precipi- 
tate on it) and put it into a clean porcelain crucible, put the 
crucible on a clay-covered triangle, and the whole on the ring 
of a ring-stand in position to be heated with a burner, warm the 
crucible gently to dry the precipitate, then put a few "pinches" 
of powdered NaKC0 3 and KN0 3 on the precipitate, and turn the 



Schoch: Introductory Chemistry 

full heat of the burner on the crucible until the mass melts: — if 
^In~ * is in the sample, the fused mass will have a green color 
when it is eokL To clean the crucible put the cold crucible in 
water to "soak" out the fused ma- 

Make suitable entries in your note book concerning the results 
obtained in this paragraph. 

The following table presents the cod tents of this article 33 at 
a glance. 

THE "SEPARATION" OF GROUP III. 

The precipitate mav contain: — Al(OH) . F- ^ . NIS a 
MnS. ZnS. 

treat with cold dil. HC1. 

Residue: test with Filtrate: MnCl,. FeCl,, ZnCl,. and A1C1 3 : add dil. HNO,. and 

borax bead, if boil, thus removing H 3 S and oxidizing Fe if present. Evap- 

reddish brown, orate to small bulk. Add NaOH solution, stir and dilute with 

Ni is indicated. water. 



Ppt. Mn (OH),, Fe (01 Filtrate: Na,Zn0,. Na,AlO,. 

a portion with NaKCO, a; Treat a portion with H,S: 

and KNOj — green color in- ppt. ZnS white . 

dicates Mn. 
(b) Dissolve another portion inj(b) Acidify another portion with 

dil. HC1 and add potassium-i HC1 and add ammonia: — 

f errocyanide : deep blue ppt. ppt. Al (0H) 5 . 

indicates Fe. 

A brief explanation will now be given of the reactions in the 
foregoing operations in this article. 

(a) The HC1 added to dissolve the whole Group III precipi- 
tate reacts metathetieally with all substances except NiS. 

(b) The reactions in the formation of the "nickel bead" are 
the following: — 

> (from the air) =XiO- - 

Xi0+XaP0,=XaXiP0 4 (phosphate of two cations!) 

This phosphate is dissolved by the molten XaP0 3 , and makes 
a "colored glass." 

When the HC1 solution of all metals except Xi is treated 
with HXO,. the H_,S and any ferrous salt present are "oxidized" 
according to the following equations : 

3BLS— 2HX0 =3S-4H 2 0-2XO. 

3FeCl,-HX0,— 3HCl=3FeCl - X0-2H.0. 

(d) The XaOH acts on the different metal compound- 
explained in Art. 3. 

(e) When Fe(OH), is dissolved in HC1 and treated with 
potassium ferrocyanide. a metathetical reaction takes place : — 

4FeCL-3K 4 FefCX) c =12KCl--Fe i [Fe(CX) 6 ] 3 , 

Prussian Blue". 

(f) When the Mn(OHV 2 is fused with XaKC0 3 and KN0 3 , 
the following reaction takes place: — 



Chapter X 141> 

Mn(OH 2 +20-J-NaKCO i ==NaKMn0 4 +H 2 0+C0 2 

(KN0 3 ) a manganate ! 

(g) When H 2 S is passed into an alkaline solution of a zinc 
salt, a metathetical reaction takes place : — 

Na 2 Zn0 2 +H 2 S=2NaOH+ZnS. 

(h) When ammonium chloride is added to a solution which 
contains NaA10 2 , the total effect produced is the same as it would 
be if the two substances from which it is formed (HC1 and 
NH^OH) were added separately. HC1 would act as explained in 
Art. 4 (b) and ammonia would then react as follows : — 

A1C1 S +3NH 4 0H=A1(0H) 8 +3NH 4 C1. 

The two reactions together would be expressed in one equation 
as follows: 

KraA10 2 +NH 4 Cl+2H0H=NaCl+Al(0H),+NH 4 0H. 

34. The General Plan of the Determination of the Cations of 

Group IV. 

This group includes all the alkaline earth metals and mag- 
nesium. The cations of all the three previous groups have been 
removed from the original solution by the procedures given in 
Arts. 28, 30, and 32; and the solution, hence, should contain only 
members of Groups IV and V (i. e., the ions Ca + + , Sr + + , Ba + + , 
Mg ++ , Na + , and K + ). The solution containing these ions ds — 

(a) The filtrate from Group I (if II and III are absent) ; 
see end of Art. 28. 

(b) The filtrate from Group II (if III is absent) ; see end 
of Art. 30; or 

(c) The filtrate from Group III, marked "Solution for Art. 
34"; see end of Art. 32. 

(d) The original solution (if Groups I, II, and III are ab- 
sent). 

The barium, calcium, and strontium ions are to be determined by 
means of the spectroscope (see Art. 35 for details) and the mag- 
nesium ion is to be precipitated, after the removal of the calcium, 
strontium, and barium ions, as magnesium ammonium phosphate 
(MgNH 4 P0 4 ) according to the procedure outlined in Art. 36. 
The removal of all the metal ions except NH 4 + , Na + , and K + be- 
fore the magnesium is determined as phosphate is necessary be- 
cause all form insoluble phosphates (see table of solubilities of 
Acids, Bases, and Salts, Chapter VI). 

35. The Flame Colorations and Spectra of Ca + + , Sr+% Ba + % Na% 

and K + . 

Vapors of compounds of these metals become incandescent at 
the temperature of the Bunsen flame, and the metals may be rec- 



l r : - z zz I:-:?. zz:::iz izzzz-zz: 



:_zzzc7 77:tz 7Z7 ::.::- zz7 zz.-~ :Z7ZZ77 z :Lt ---~z 7_:: : ::r 
zziy 7~z zzt7 ;:tz_z :z zizzli I." :i'. ?:"" ~tz z ziz 
Mf zzz_ z: Z7 -zzziTlt zr.IzTi.Zi Zz: 7.7 7— : zzzzli zi~- 
-■r-.z. : z_ -r-1 iz. jz.z'.i Z zz: 17 :z I 7rzz :: zz if:.: :':.: 
i z - tztzz 7 77 i i .1 :._- _z z A _ f ~ : : 7: z zzz7 :•: . : 7= ii * :i 
below: 



:.i-.--;:: : — _ Z7-77. 

?iz :-— 1.::." " 



- - 7- 7 7= :r:- ^tzt- zzzzz 7:7" 7 :-::::: :ze zz- 
from oQl~ necessary, with mix t ur es contain in g several of 

these metals, to view the- colored flame through a spectroscope. 

Tz 7 77 zz z - z -7 - 7.7 :^:7:' v.: zrz: 77 z z^ .zz- 

components are relatively f e w in number, and each one is of a 
:olor ? hence the spectra of the incandescent vapors 

: z -7 zz Z-7 177 7 1- «z::i ::' zzz z z ztz zziz7 :-:z-- zz 
-7.7 -':. 7 - - 7 : z.:si 7 7rz :: zz :- :7 zz z :zzz 

7Z77ZZ7 " "-Z 7 77--- ZZt7-Z7 /ZTZZ: 7 ZZf 777 Z- 

tained at particular points in the "range" of the sunlight's 

- . - - zzzt rzzzz 

"1- ZZZ- "ZZ7Z ZZ 7' ZZ ZZZ7 ZZ Zi.Z ZZ77. Z7 7 

zzr zz: ":7-- 7z-5 : zzz zz - 7 — 7 7 : : - z :z.7 77 zer 
places simultaneous with the lines of the other metals at their 

"77'" -7 7.ZZ. - Z-r ZZ - Z "7 ~ - 7 Z Z 7Z : Z7 7 7Z77ZZZ - Z 

these metals are thus """analyzed" at a glance. 

A char - . g the pwatiwiB and colors of the fines eharacter- 

:f the metals z. and K" should be found 

z:i7 :zr -7 ; z:zz :' 7 7 ■• • "- 7 :' -z. - z : zz zz- z : zz':z 

7Z7 ZZZ7 77 z'_ 1 - Z77 7 - 7 Z "7> ZZ7Z Z. Z =7 7 7Z " '7"- 

: : - 
- - - -7, : -zz — 

MmmiptUmHtm for the Flame or Spectroscope Ttst. — Clean a 

platinum wire mechanically as thoroughly as possible, then hold 

die Same of a Bunsen burner to a imparts any color 

-- 7:- zz- z z i zz z :zz:^ fzzrrZzr 7:z.zz. ~'r z7 z 
•:•:•: zzzzfzsz ":~ :zz7 7 z zzz: /zzizzz zizzzz: zzz 
z: 7zz7 : :: :;.- zizz^ 7z " - - z zz z.z z lztzz77 zzzlI 
Z77 rz — . zz —77 zzzzzzs z: ziz z: :izs z:tz- _" — zzzzzzz 

; . . . z - - - 7 

z:ii ;- Z 77- 7 " ' " 

dame indicates the metal placed with the color in the list above. 

■ . ~ " 

f:7 — zz : tzz«:zz77 : 7^ 

: : 7 -77- z — -zzz: L= z-77- zz: z 7;:^- :z^ 



Chapter X 151 

"scale": — the prism should be moved until a certain number on 
the scale — say, 10 or 50 — is at the sodium line. The positions 
of the lines of other metals are usually given with reference to 
the sodium line. 

Sodium compounds are so widespread in nature that almost 
all substances contain enough sodium to give the sodium line 
when heated in the Bunsen flame; but sodium is not to be con- 
sidered as present unless enough of it is present to color the 
flame heavily and persistently. 

Potassium — a deep red line to the left of the sodium line — 
(at 7.9 or 17). 

Calcium — two very broad and heavy lines, close to the sodium 
line; green to the right and red to the left of sodium. Several 
other light red and green lines are also present. 

Strontium — several heavy (and several light) red lines (to the 
left of sodium), the number of which is greater than the red lines 
of calcium. 

Barium — several heavy (and several light) green lines (more 
than for calcium) and also a few light red lines. 

36. The Identification of the Cations of Group IV. 

(a) To identify the Ca + + , St* + , and B& + + ions, proceed as 
follows: Clean a platinum wire as described in Art. 35, dip it 
into the solution for Group IV (as described in (a), (b), and 
(c) of Art. 34 and test for both flame coloration and spectroscopic 
lines. Be careful to obtain a very positive test for these ions 
(Ca ++ , Sr ++ , and Ba + + ) before reporting them. It may be neces- 
sary to evaporate the solution you are testing to smaller bulk, in 
order that the concentrations of these ions may be larger. 

(b) The removal of the Ca + + , Sr + + , and Ba + + ions : In order 
to identify the Mg + + ion, it is necessary to remove the Ca + , Sr + + , 
and Ba + + ions from the solution, if the spectroscope has proven 
them to be present. (See again last part of Art. 34.) To do 
this, proceed as follows : The solution must contain NH 4 C1 and 
enough NH 4 OH to turn red litmus blue (the NH 4 C1 must be 
present to prevent the precipitation of the Mg ++ as Mg(OH) 2 ). 
If these substances are not present in the solution, they must be 
added in proper amounts. Then put the mixture into a small 
flask or beaker, heat it to boiling, and keep it boiling while adding 
the following reagents drop by drop until, in clear portions of 
the liquid, additional drops produce no more of the precipitate : 

(a) If Ba + + or Sr + + is present, add ammonium sulphate solu- 
tion, (im 4 ) 2 S0 4 ; 

(b) If Ca + + is present, add ammonium oxalate solution, 
(KH 4 ) 2 C 2 4 ; 



152 - hoch: Ixteoductoey Ghkmxbtky 

(c) If Ba' * and (V ~. or Sr* * an are present, add 

first ammonium sulphate, in sufficient amou: md then 

ammonium oxalate in sufficient amount (only a little of the lat- 
ter will be needed!) Precipitates of Ba>' SrSO*, and of 
4 are formed by metathetical reaction. 

Allow the precipitate to settle, but do not allow the liquid 
to cool ! If it has been boiled enough, the precipitate will settle 
rapidly, and afterwards will not pass through the filter. De- 
cant the clear liquid upon a clean filter paper, and collect the 
filtrate in a clean small fi 1 another drop of the reagents 

just used to ascertain if all the alkaline earth cations have been 
precipitated. 

num. — To the liquid ob- 
tained in (b) add 2-5 c.c. of sodium phosphate (X; IIP«» 4 i. cool 
the liquid if it is still warm (by allowing the tap-water to flow 
over the outside of the flask se the flask with a stopper, and 

shake vigorously until a dens» :ine (not flocculent!) pre- 

cipitate appears. Sometimes 3-5 minutes of shaking are neces- 
sary. If a precipitate with the correct a: - obtained, 
nt in the sample under consideration. The pre- 
cipitate is formed by metathetical reaction : — 

^+ira 4 0H+Na s HP0 4 ==£Mgl»H 4 P0 4 +2NaCl+^0. 

Filter this precipitate off, saving the filtrate and mark it "Solu- 
tion for Art. 

The following table presents the foregoing directions in out- 
line : — 

THE "SKPJJtATK 

The filtrate from the procedi: rte. 28. 3<>. or 32 may con- 

tain Ba' - r _ <and members of Group V 



Make flame and spec- 
troscopic tests on 
concentrated solu- 
tion for Ba ++ . Sr ++ . 
and Ca* + . 



Remove the Ba**. Sr**. and Ca + * bv means of XH 5 C1 
NH,OH. \~H; T SO;. and XH ; C/' T . Filter off the pre- 
cipitates of BaS0 4 . SrS0 4 , and CaC : 



To this filtrate add Na,HP0 4 solution: a dense crystalline 
precipitate after 3-5 minutes shaking) indicates Mg* + . 



Filter and save filtrate for Group V 



37. The Identification of Group V. 

The solution obtained in Art. 36. labeled "'Solution for Art. 
37/* may contain Xa" and K~. In tb ~ will not 

as is often done, but they will be identified by a 
? tests, made s g to the procedure of Art. 35. 

In the identification of the catic : Nip IV. the ion= 

and K~ may have been determined along with the others. If post- 



Chapter X 



153 



tive tests have been obtained for Xa + and K + , it is not necessary 
to identify them again here. If, however, they have not been de- 
termined, the solution should be evaporated to small bulk (practi- 
cally to dryness) ; and the spectroscopic test for Na + and K + made. 

Great care should be exercised in the determination of Na + : 
even very small amounts (from the air, etc.) will give tests for 
sodium, and hence only a very prominent sodium line should be 
taken to indicate the presence of Na + . 

The test for NH 4 + should only be made on the original un- 
known solution handed you, for its presence at the end of our 
qualitative procedure would mean nothing since ammonia and 
ammonium salts have repeatedly been added to our solution as 
reagents. The original solution should be tested in the following 
manner : 

Put a pinch of the original dry sample (or solution) into a 
test-tube, add a few drops of sodium hydroxide solution, and 
warm the mixture. If ammonium compounds are present, the 
mixture will emit the odor of ammonia, — produced according to 
the equations: 

NH,X-J-lSraOH=NH 4 OH-f^ T aX 
NH 4 0H=XH 3 +H 2 

The following table presents the procedure in outline: 



THE IDENTIFICATION OE GROUP V. 



Evaporate solution to small bulk; make 
spectroscopic tests for Na + and K + ac- 
cording to procedure of Art. 35. 



Original unknown samplefis^treated with 
NaOH: an odor of ammonia proves 
presence of NH 4 + . 



38. Determination of the Anions. 

As mentioned in Art. 26, this procedure has been designed 
merely for the following compounds of the common metals: 
oxides, sulphides, carbonates, phosphates, nitrates, acetates, sul- 
phates (except the insoluble sulphates) and chlorides (except 
AgCl). The procedure in Arts. 28-37 enables us to ascertain 
what metals are present in a substance to be analyzed, but when 
the substance is not merely a metal (or an alloy), but a com- 
pound, it is necessary to ascertain what the metals are com- 
pounds of. The first thing that gives a clue to the nature of 
these compounds is their solubilities: — this knowledge together 
with a knowledge of the cations in the compound enables the 
analyst to make certain conclusions concerning the possible 
nature of the compound. Thus if the substance is soluble in 
water and contains the cations Ca + + and Ba + + , then it cannot 
be a sulphide, oxide, carbonate, phosphate or sulphate; and only 
the nitrate, chloride, and acetate ions should be tested for. 

Only "water-soluble" compounds should be tested for the nitrate 
ion, acetion, sulphate ion and chloride ion according to the special 



154 Schoch: Ixteoductori* Chemistry 

directions given below. Since such "water-soluble" substances 
may also be sulphides, carbonates, or hydroxides, it is necessary 
to note in connection with these other tests (1) if much of an 
acid is necessary to render the solution acid to litmus (presence 
of hydroxides), or (2) if a gas is evolved when an acid is added 
(H 2 S— or C0 2 ). 

If the substance is an insoluble sulphide, it will either evolve 
H 2 S when treated with an acid, or solid sulphur will be formed. 
If it is a carbonate, it will effervesce when treated with an acid 
but the gas evolved will be odorless and colorless. 

Any "water-soluble" substance which dissolves "in acids" with- 
out the evolution of a gas or without the formation of sulphur, 
should be either an oxide or a phosphate because nothing else 
is to be given to the student in this work. But this holds also 
for all substances of common occurrence. Such substances should 
be tested for the phosphate ion by method (b) given below. If 
it is thus found not to be phosphate, then it must be an oxide. 

39. Special Tests for Anions. 

The Sulphur Ion. — Acidify the original aqueous solution with 
a few drops of dilute hydrochloric acid and add a few drops of 
barium chloride solution. No other anion gives an insoluble 
barium salt under these conditions. 

The Nitrate Ion. — To the original aqueous solution add an 
equal volume of concentrated sulphuric acid and allow the mix- 
ture to cool. Then pour care fully upon it a solution of ferrous 
sulphate in such a manner that the solutions will not mix, the 
ferrous sulphate solution being on top. A brownish-black ring 
(FeS0 4 :X0) at the boundary of the two solutions indicates the 
presence of a nitrate. 

The Chloride Ion. — Acidify the original aqueous solution with 
dilute nitric acid and add silver nitrate solution: a white precipi- 
tate indicates the presence of a chloride; if the precipitate has a 
slight yellow color, it may indicate the presence of a bromide ; and 
if the precipitate is tinged deep yellow, it may indicate the pres- 
ence of an iodide. 

If either of the last two substances is thus indicated, it becomes 
necessary to make use of special directions, to be obtained from 
the instructor, to test for the presence or absence of the chloride 
ion. 

The Phosphate Ion. — (a) If the sample is soluble in water, 
it may be tested for phosphates by adding ammonium chloride, 
ammonium hydroxide and magnesium chloride. A dense, crystal- 
Line, white precipitate (of MgXELPOJ indicates the presence of 
phosphates. 

(b) If the sample is not soluble in water but has been dis- 



Chapter X 155 

solved by means of acids, the phosphate ion must be tested for in 
the following manner: dissolve the solid in dilute nitric acid, pour 
about one cubic centimeter into a clean test-tube, warm it to "blood 
heat/' then add from two to three cubic centimeters of am- 
monium molybdate to the hot solution, and then let it stand for 
about five minutes. A yellow precipitate of ammonium phospho- 
molybdate, (NHJ 3 P0 4 (Mo0 3 ) 12 indicates the presence of a 
phosphate. 

The Carbonate Ion.— Place some of the original solid or aqueous 
solution into a test-tube and add a small quantity of dilute hy- 
drochloric acid. If considerable quantities of gas are evolved, the 
gas should be tested by suspending a drop of clear calcium hy- 
droxide or barium hydroxide solution from the end of a glass tube 
in the upper part of the test-tube. A white cloudiness (of CaC0 3 
or BaCOg) in the suspended drop indicates the presence of a 
carbonate. 

The Acetate Ion.— (a) Add a few drops of a dilute, slightly 
acidified solution of ferric chloride (the stock solution of ferric 
chloride contains the proper amount of acid) to a little of the 
original solution: a reddish coloration indicates the presence of 
an acetate. On boiling this solution, a reddish-brown precipitate 
of ferric hydroxide is usually obtained; sometimes a deep reddish- 
brown solution results. 

If a phosphate is present, a light yellow precipitate will be 
formed at once in the cold and not a reddish solution. If a car- 
bonate is present, a reddish-brown flocculent precipitate will be 
formed at once in the cold, but not a reddish solution. To re- 
move the carbonate so that it does not interfere 1 with the acetate 
test, proceed as follows : to the original solid or solution add dilute 
hydrochloric acid drop by drop until, upon warming, carbon diox- 
ide is no longer evolved. Care should be taken not to make the 
solution but very slightly acidic. Then add a few drops of ferric 
chloride solution. A reddish solution indicates an acetate. 

(b) Add to the original dry sample a mixture of equal vol- 
umes of concentrated sulphuric acid and of alcohol. Stir and 
warm the mixture: a fruity odor indicates the presence of an 
acetate. Only pure alcohol should be used in making this test 
or the fruity odor will be obscured. This test requires consider- 
able training and technical ability. 

40. Conclusion. 

After examining a substance in accordance with the directions 
in Arts. 27 to 39, inclusive, a definite conclusion should be reached 
by the student concerning the nature of the substance as a whole, 
and he should look into some large text-book for a description of 
the compound to confirm his conclusion. The compounds given 



156 Schoch: Introductory Chemistry 

the student should be important in themselves — as a whole. Thev 
should be commercially important salts or natural compound's 
(minerals), and the student should strive to make himself familiar 
with their appearances and u- 

Questions on Chapter .X. 

1. (a) In what respect does a solution of hydrogen sulphide 
in water, which contains also some of a strong acid, differ from a 
solution of hydrogen sulphide which contains no strong acid? 
Explain or disease this difference adequately. 

(b) When a solution of hydrogen sulphide in water is added 
to a pure zinc sulphate solution, a precipitate is obtained: but 
when some of a strong acid is first added to the zinc sulphate 
solution and then the hydrogen sulphide solution is added, no 
precipitate is obtained : point out definitely why a precipitate is 
obtained in the first case and none in the second. 

(c) A solution of a copper salt will oive a precipitate when 
pure hydrogen sulphide solution is added to it and also when a 
hydrogen, sulphide solution which contains some of a strong acid 
ifl added to it (or when some of a strong acid is first added to 
the copper salt solution and then the hydrogen sulphide solution 
is added) : point out why I ict salt solution behaves differ- 
ent from the zinc salt solution in the instances just cited. 

2. A druggist discovered that his stock of alum (a double 
sulphate of aluminium and potassium) had been contaminated 
with Epsom salt (magnesium sulphate) : name a general reagent 
with which the aluminium and the magnesium may be separated 
from a common solution and secured in two separate portions; 
and describe how to do this. Write all questions for the meta- 
thetical reactions occurring in this work. 

3. Xanie another common reagent which may be used with the 
solution of the two substances in question 2. 

4. Make an outline of the separation of Group III in the pro- 
cedure for the analysis of metals. 

Give the equation for the precipitation of magnesium in 
the scheme for the determination of metals. Why does one 
hydrogen atom appear in the formula of the substance commonly 
designated as sodium phosphate ? Why is aluminium sulphide 
not obtained when an aluminium salt is treated with a sulphide? 

6. Describe briefly how to test an unknown to determine if 
it is a sulphate. Would you make this test on a substance which 
is insoluble in water? Xame the reagent that is used to test 
an unknown to ascertain if the latter is a phosphate in case this 
unknown is insoluble in water. 

7. (a) Calcium phosphate is sriven out as an unknown to 
be analyzed. State by what means it will be dissolved and .give 



Chapter X 157 

the equation for the reaction which takes place during the dis- 
solution of this substance. 

(b) As this solution is taken through the regular course of 
analysis, where will the calcium be precipitated? Explain as 
fully as possible why it is precipitated at this point instead of 
at the usual place. 

8. An unknown consists of water soluble salts of copper and 
of cadmium : describe all that will occur as this solution is worked 
with in accordance with the direction for the determination of 
the cations, being careful to describe the color or general ap- 
pearance of all the precipitates or anything that may be seen. 
Finally write all equations occurring in this work that you are 
prepared to write, and for the remaining reactions state the com- 
position of the main substances formed. 

9. The composition of a yellow powder — which is either -an 
oxide or a salt of a common metal — is to be determined : this 
substance is found to be insolubJe in water; hydrochloric acid 
acts upon it but does not convert it to soluble substances; while 
dilute nitric acid dissolves it readily. The procedure for the 
determination of the cation shows that in Groups I and II only 
lead is present. 

(a) State, in their order, very briefly and definitely, the re- 
sults this solution will give while it is examined according to 
the directions for both the first and the second group. Before 
answering this, read (b). 

(b) You should end the procedure in the first and second 
group as soon as you have experimental indications that the rest 
of the procedure is unnecessary; state what experimental result 
induces you to discontinue the procedure of Group I. Do the 
same for Group II, being particularly careful to give all your 
reasons here. 

(c) Why does this solution give a precipitate in Group II? 
What is the color and quantity of this precipitate ? 

(d) Besides giving the precipitate in Group II, this solution 
may turn milky white; what is the substance that makes this 
solution white; what two substances act upon each other to pro- 
duce this "white" substance? 

(e) In general, the unknowns that you are to analyze may 
contain the metals in one of the following forms: as a free metal 
or alloy, as an oxide, as a nitrate, chloride, sulphate, acetate, 
carbonate, sulphide, or phosphate. Judging from its behavior 
above, in which of these forms may the lead in this sample be 
present? Give your reasons why it could not be in the forms 
excluded. The yellow powder is litharge, PbO, a commercially 
important substance. 

10. In what respect does a solution of ammonia which con- 
tains also some of an ammonium salt differ from an ammonia 



- hoch: IxTBODrcioBT Chemistby 

solution which contains an ammonium salt? Explain or d:~ 
this difference _ a w what yon know about it. 

(b) When pure ammonia solution is added to a magnesium 
sulphate - :dned: but when an am- 

monia solution which contains also some of an ammoniuir 

_ -:nm sulphate solution, no precipitate is ob- 
tained : point out definitely why a precipi: d the 
firs: ::d none in * nd. 

- ition of an aluminium salt will give a pi 
when pnre ammonia solution is added to it and also when an 
ammonia solution containing some of an ammonium - - :ided 
int out why an aluminiu ~ lution behaves differ- 

ent from a magnesium salt solution in the ix ted. 

11. Brass is an alloy of copper and zinc. By what means 
would you produce soluble compounds of these metals from 
From this solution either one or both of these metals may be 
precipitated separately by means of two very common - _ 
name one of these reagent* and state what you must do to secure 
the two metals in two separate port ange the 
copper to copper nitrate and then change as much of the zinc as 

le to zinc chloride. Write all equat: :he met; 

- occurring in this work. 

12. Xanie the other of the two common re;. hich mav 
be used in the solution in question 11 to separate copper from 
zinc out of the above solution and proceed with the use c: 

_ nt to do again what is called for in question 11. 

13. [Make an outline of the separation of the common m 

-he formula? of all the precr 
in each precipitated group: and give the equation for the pre- 
cipitation of one metal in each of * - ope. 

14. Enumerate all the fact* made use of in the analytical 
outline to reveal the nan:: -muth or : .In the 

for bismuth, what reaction occurs? What is the name 
of this i fa reaction? Point out th d% of the name. 

"What substance must be : :. the solution in order to pre- 

- reaction in the case of bismuth J - oi ' a mat- 
ter as fully as you can. 

15. What observations and what additional tests would en - 
you to decide that snfasi is a carbonate? If an unir 
compound soluble in water has been found to be a compound of 
copper, what common ani best far? Why - est 
only? Describe briefly how ~: : ; : for chlorides. Describe briefly 
how :; test for i 



Chapter XI 159 



CHAPTER XI. 

ELECTROLYSIS— THE CHEMICAL CHANGES AT THE POLES 
OF ELECTROLYTIC CELLS. 

Note. — Since in connection with the study of the preceding 
chapter on qualitative analysis it may be desirable to spend a con- 
siderable number of hours in the laboratory on "unknowns/' it is 
advisable to present the following chapters (Chapters XI and XII) 
in the class room. It will be found that most of the experiments 
can best be performed on the lecture table instead of having the 
students perform them in the laboratory. 

1. Electrolysis. 

Electrolysis is the chemical decomposition of substances by 
means of a direct electric current. The latter must naturally be 
forced through the electrolytic cells by some outer agency, such 
as a battery or a dynamo. 

2. The Algebraic Signs of Poles. 

An electrolytic cell has its poles marked in accordance with 
the kind of electricity sent into it. The negative pole is also 
called the cathode, because the cation's move toward it while the 
current passes, and the positive pole is also called the anode for 
the corresponding reason. 

A battery cell or a dynamo (which supplies current) has its 
poles marked in accordance with the kind of electricity which it 
supplies. Thus, the positive poles of a battery cell or a dynamo 
is that pole at which positive electricity flows out of it. When 
this pole is connected with a wire to the pole of an electrolytic 
cell, the latter is made the positive pole, because positive elec- 
tricity is sent into it at this point. 

The difference in the assigning of signs to the poles of battery 
and electrolytic cells, respectively, corresponds to the difference 
in our use of these cells : — the battery cells are used to supply 
current and the poles are marked to show what they supply; while 
electrolytic cells are cells into which we send current to produce 
results, and their poles are marked to show what we send into 
them. 

3. The Electrolysis of a Solution of Zinc Chloride. 

Experiment. — Secure a liter-beaker full of an (approximately) 10 per 
cent solution of ZnCl,. Suspend a strip of sheet brass about 2 inches wide 
and 8 inches long into it on one side, and dip into it a carbon pole pre- 
pared as follows: A piece of wide glass tubing about 1£ inches wide and 



160 S hoch: Ixteoductoby Chemistey 

10 inches long is iitted with a rubber stopper with two holes, one for an 
electric light carbon or a similar graphite rod. and the other for a piece 
of narrow glass tubing. Let the graphite rod extend into the tube almost 
to its other end. Trim the end of the carbon rod projecting outside of 
the tube so as to leave a flat strip of the width of the carbon rod and 
about I inch in thickness. With the aid of "burette screw clamp." the 
end of a copper wire for th<? electrical connection is clamped to this flat 
end of the carbon rod. Secure a narrow glass tube about 24 inches long, 
bend it twice at a right angle so that when everything is properly assem- 
bled this narr _. :ube may extend from the under surface of the 
stopper over the edge of the beaker to the bottom of a bottle or cylinder 
standing beside the beaker. The latter should serve to collect the chlorine 
gas which is to be evolved: Secure such a vessel and put a wad of cotton 
in its neck. This will serve to prevent the chlorine from escaping into 
the room. Secure a suitable source of direct electric current with an 
electric pressure of S to 12 volts. Connect the brass strips to the nega- 
tive pole of this •current source*' and the carbon rod to the positive pole, 
thus making the brass rod the negative pole and the carbon rod the posi- 
tive pole of the electrolytic cell. When connection is made so as to com- 
plete the circuit, a sufficiently large current should flow so that in a few 
minutes the brass strip will be coated with gray zinc, and enough chlorine 
will be evolved to be seen in the cylinder. 

4. The Present-day View of Electricity. 

Before considering, in detail, the changes in the preceding, it 
will be profitable to learn how electricity is now pictured in the 
minds of men who know something about it. It is thou_ 
something like a very lig: nposed of particles called elec- 

trons. All substances contain these electrons — they are a com- 
ponent of all matter. Even substances which appear to us * 
electrically neutral contain electrons; they do not appear to be 
"electrically charged*'* even though they contain electrons, be- 
cause in all electrically neutral substances the ''•electron-pressure'' 
is the same and hence electrons do not pass from one to the 
other. — ii>: us lies which are at the same temperature do not 
warm or cool each other — i. e., they do not transfer heat from 
one to the other. 

When substances contain more electrons than they contain in 
the "neutral" state, they are said to be charged negatively. When 
"neutral" substances have lost one or more of their electrons, 
they are said to be charged positively. 

Monovalent anions — such as the chloride ion (Cl~). the nitrate 
ion (KO,~)j the hydroxyl ion (OH~) — are considered to be com- 
pounds of material atoms denoted by the symbols plus one 
tron more than they have in their neutral state. Bivalent 
anions — such as (0~~ S0 4 ~~ ) — are compounds of the ma: 
atoms plus two electrons, etc. Monovalent cations — such as 
Ag* } Na* K~. H~ — are atoms of the respective elements which 
have given up one of the electrons which they contained as neu- 
tral substances. Bivalent cations, such as Cu* ", Pb" *, Ca _ ~. have 
given up two electrons, etc. 



Chapter XI • 161 

What is commonly denoted by "the electric current flowing 
through a circuit" is the flow of positive charges which have here- 
tofore been assumed to exist: this direction of flow is one decided 
upon by convention. Instead of this flow of positive charges, we 
now consider the electrons (negative charges) as flowing in the 
opposite direction. Algebraically, these two expressions amount 
to the same thing, because a negative quantity moved in a nega- 
tive direction is equal to the same quantity with a positive sign 
and moved in a positive direction. Hence, throughout the con- 
sideration in this book, we shall consider only the direction of the 
flow of negative charges or electrons, and we shall always speak 
of it as "the direction of the electron flow." Electrons by them- 
selves are designated by a minus sign placed within brackets; e. 

g; (-) 

5. Consideration of Changes That Have Taken Place in the Elec- 

trolysis of Zinc Chloride. 

We shall now consider the changes that have taken place in the 
electrolysis of zinc chloride. The facts that were observed by the 
student were the changes that took place at the poles of the elec- 
trolytic cell: (1) at the negative pole (brass pole) grey metallic 
zinc was deposited, and (2) at the positive pole (carbon pole) 
chlorine gas was evolved. The following discussion will seek to 
present the explanation of the observed phenomena from the view- 
point of generally accepted theory. At the brass pole, negative 
electricity (electrons) were forced into the sheet brass and en- 
tered the layer of solution next to it. These electrons reacted 
(or combined) there with the only substances present with which 
they could react — the Zn ++ ions — according to the equation 

Zn ++ +2(— )=Zn° 

Simultaneously with this action the opposite kind of a reaction 
was going on at the carbon pole. The action of the battery cell 
or dynamo (think of it as an electric pump) draws electrons out 
of this region, causing the chlorine ions next to the carbon pole 
to give up their electrons and change to the neutral form or 
gaseous chlorine. The reaction that takes place is 

2C1-— 2(— )=CL° 

It should be noted that there were withdrawn from the carbon 
pole as many electrons as were sent into the brass pole; the bat- 
tery cell or dynamo, in effect, has merely served "to pump" these 
from the carbon pole to the brass pole. 

6. The Unfeeen Third Action of the Cell; The Transport of Ions. 

The discharge of cations at the cathode leaves the portions of 
the solution from which they are taken momentarily with more 



B DOT : IaTBUDUC 7 7V 7£ 1 1 1 > TET 

anions than cone- i :he anode the 

diaeL -.. /ition momen- 

tarily with more cations than correspond to the anions present. 
On account : _ unbalanced uric 

. " ~ " ' - " " : in adjacent 

and both m kO they are in the "same dro: 

liquid; i. e.. until they have formed "neutral" drops. — drops 
which contain an equal number of positive and negative dm 
the anions thus displaced in these adjacent di :he same 

with the db in the drops still farther - At the same 

time I " . - which remain unbalanced at the ancx: 

draw together with the anions in drops adjacent to then, 
two tendencies sasA each other, and. extending from eathc 

_• about I -.11 the cation- - 

the cat :' all the ids the anode. These shifts 

mov^ - d the poles": thus the 

dona next to the r - me more dilute. Since some kinds 

-ily than oth :he mutual attra 

ste? than the other kind, and fa 
the imp* _ on may be more rapid at one pole 

than at tib 

by means of a model, draw with the 
aid of a small coin or a compass a row of conv_ 
about j inch diar. "irely across the nppei 

of writing paper - width. 1 

are * lea a row of adjacent 

drops extend.: i Pat in each upper half 

and in each lower half a minu- 
to represent an equal number of positive and r. - 
each drop. Cut the strip of r m the sheet, and split it 

into two - - ten of the c: 

theieat f the si I with the ends 
o f the sheet underneath. 
7 i cj ui oau n l ft b e c haig c rf a positive ion, fold the left end 
of the upper str:^ - - n place the first half circle underneath 
this strip: do the same with the last half circle on the right end 
of the lower strip. Next move the upper strip J of the diameter 
of the circles to the left, and the lower J of the diameter to the 
right, and note that the left circles in the tw meet each 

other again. Note that the le:~ - f both detached strips are 
only i diameter from the left-hand edge of the original sheet 
which they rest, while the right ends are j diameter from the 
right-hand edge of the original sheet. This indicates that there 

- "red substance at both poles and that the 
of dissolved substance on the risrht is three tim _ *s on 

the left 



Chapter XI 163 

7. Effect of Prevention of Transport of Ions. 

One more question needs to be considered: would these changes 
take place if the two poles were placed in separate beakers so 
that the liquid would not extend from one pole to the other? 
The answer is: strictly speaking, these actions will take place at 
first, but will cease before appreciable amounts of ions are dis- 
charged, because the excess of anions remaining in the beaker in 
which cations are discharged, charge this region electrically nega- 
tive, and the excess of cations remaining in the beaker in which 
the anions are discharged charge that region positively, and these 
electric pressures act counter to the electro-motive force which 
impels the current; hence the current will flow only until this 
''back pressure" in the beakers is equal to the applied electro- 
motive force. 

8. The Electrolysis of Hydrochloric Acid. 

Experiment. — Secure a 1 -liter beaker full of dilute hydrochloric acid 
and dip into it the carbon poles used in the preceding experiment, and 
dip into it also a hydrogen pole prepared as follows: a glass tube sim- 
ilar to the one used to make the carbon pole in the preceding experi- 
ment is fitted with a two-hole rubber stopper. One hole should be such 
as to admit a stout lead wire (diameter £ inch or more), which should 
extend almost to the other end of the tube and be bent into the form 
of a spiral near its free end. Into the second hole of the rubber stop- 
per should be fitted a piece of narrow glass tubing, about 24 inches 
and bent so as to extend from the inner surface of the rubber stopper 
into the water in a vessel standing beside this electrolytic apparatus: 
by means of this tube, hydrogen is to be collected in a bottle inverted 
over water. Connect the carbon rod to the positive pole of the source 
of direct current, and the lead pole to the negative pole, and apply such 
an electromotive force that a bottle full of hydrogen may be obtained 
in a short while (10 minutes). Test the hydrogen by igniting it. 

In this case, hydrogen ions are the only substances present 
which can combine with the electrons. They react at the cathode 
according to the equation — 

2H + -f2(— -)=H 2 °. 

At the other pole, where the electrons are "drawn out of the 
solution," the chlorine ions again give up electrons. It appears 
from a comparison of this experiment with the preceding that 
the action of the liberation of chlorine takes place irrespective 
of the kind of an action taking place at the other pole. 

9. The Electrolysis of Dilute Sulphuric Acid. 

Experiment. — Prepare another "lead pole" just like the cathode in the 
preceding experiment, and dip this and the cathode from the preceding 
experiment into a 1 -liter beaker full of dilute sulphuric acid. Attach 
the connecting wires to sources of direct electric current, and apply a 
suitable electromotive force to obtain a fairly rapid evolution of the 



3 64 - soch: Introductory Chemistry 

gases at the poles. Collect the hydrogen and oxygen obtained in 100 c.c. 
cylinders and note, roughly, their relative rates of evolution. 

At the negative pole, hydrogen is evolved as in the preceding experi- 
ment, but at the positive pole, oxygen is obtained. Identify these gases 
by any suitable means. 

In order to understand this liberation of oxygen at the positive 
pole, we must realize (1 ) that water is undoubtedly ionized partly 
into H" and 0" ~ ions: and (2) that the discharge of 0~ ~ ions 
would be just as much the action of the positive pole (anode!) 
as the discharge of S0 4 ~ ". Since nothing but oxygen is obtained. 
we conclude that the oxygen ions from water are more easily dis- 
charged than the S0 4 " " ions; hence the action at this pole is rep- 
resented by the equation — 

20--— ±(— )=0 2 ° 

or 20--=O t °+4(— ) 

10. The Electrolysis of NaJSO, Solution. 

Experiment. — Secure a 1 -liter beaker full of a concentrated sodium 
sulphate solution: dip into it the two 'lead poles" used in the electrolysis 
of dilute sulphuric acid. Apply a fairly high electromotive force so that 
a fairly large current will flow in spite of the relatively poor conductivity 
of the salt solution. Oxygen and hydrogen will be obtained as with dilute 
sulphuric acid. 

In this solution we have, for cations, both H~ and Na + ion>. 
and the cathode action apparently might take place with either 
one of these; the fact that hydi 9 gas i£ btained indicates that 
hydrogen ions are more easily discharged: and hence the 
action is represented by the equation — 

o H -_2( — )=1! 

The action at the anode is the same as in the preceding ex- 
periment. 

Dip strips of blue and red litmus paper into each one of the cups 
and also test some of the original electrolyte: — the liquid around the 
cathode will turn litmus blue and that around the anode will turn lit- 
mus red. These effects are due to the presence of OH- and B> ion- 
spectively. 

Both of these ions are the remaining parts of the molecules of water 
of which the H" and O - - ions, respectively, has been discharged. 

11. The Electrolysis of Copper Sulphate Solution. 

Experiment. — Secure a 1 -liter beaker full of a moderately concentrated 
solution of copper sulphate (a 10 per cent solution i . Put into it — sus- 
pended from the edge- 1 — a strip of sheet brass about 2x8 inches and con- 
nect it to the cathode. Dip into the solution the '•lead anode"' from the 
preceding experiment: electrolyze the solution with a moderately large 
current, but avoid a current so large as to form a '"spongy" copper de- 
posit. Xote the copper deposited, and identify the gas obtained at the 
anode. Write the equation for both pole actions. 



Chapter XI 165 

12. The Electrolysis of a Solution of Sodium Chloride. 

Experiment. — Secure a 1 -liter beaker full of a fairly concentrated 
sodium chloride solution (20 per cent), dip into it the "carbon anode" 
from Exp., Art. 3, and the lead cathode from the preceding experiment. 
Turn on the current, identify the products, and write the equations for 
the pole actions. 

13. The Complete Independence, from Each Other, of the Actions 

in an Electrolytic Cell. 

The fact that both in hydrochloric acid and in dilute sulphuric 
acid, the same cathodic action — i. e., the discharge of hydrogen ions 
— took place, although the anode actions were different, and, again, 
the fact that- both in zinc chloride solution and in hydrochloric acid, 
the same anode action — i. e., the discharge of chlorine ions — took 
place, although the cathode actions were different, these and other 
such illustrations obtained from the above experiments show that 
the nature or kind of a change taking- place at one pole of an elec- 
trolytic cell is independent of the nature or kind of a change tak- 
ing place simultaneously at the other pole. 

Furthermore, it is plain from the explanation in Art. 6 that 
the third action in every cell — i. e., the electric transport of 
ions — does not move certain ions, but moves any ions which are 
present. Thus in the electrolysis of sodium sulphate solution, 
the ions present in largest amount, and hence mostly avail- 
able for this electric transport or "third action of the cell" are 
]^a + and S0 4 ~ ~ ions, and these are the ions which take part in 
this third action of the cell, though neither one of them takes part 
in the other two actions — the discharge at the poles. 

From all this it is evident that the three changes in an elec- 
trolytic cell are distinct and independent of each other. This is 
shown very strikingly by the arrangement in the following ex- 
periment : 

14. To Demonstrate the Quantitative Relation Between the Hydro- 

gen and Chlorine Evolved Simultaneously by Electrolysis. 

Experiment. — Secure two small porous earthenware cups, 3 to. 4 inches 
in height and H to 2 inches in diameter. Dip their upper edges in 
melted paraffin to a depth of one inch in order to close up the pores in 
these parts of the cups. Secure two rubber stoppers large enough to fit 
these cups. Perforate one with two holes so as to admit a small graphite 
rod, and a narrow piece of glass tubing; perforate the other two with 
holes so as to admit a stout lead wire, and also a piece of narrow glass 
tubing. Secure three glass jars or beakers, two of which are to be filled 
with water and are to be used to collect gases — in burettes, over water — 
as shown in the accompanying sketch. The third is to be filled with a 
saturated solution of salt — sodium chloride — and into this are to be 
placed the porous cups. Secure the rest of the apparatus and connect 
it as shown in the accompanying sketch. Note that the ends of the con- 
ducting tubes under the burettes are drawn out to fine openings, bent so 
as to be horizontal, and placed as high in the water as possible. 



166 



Schoch: Introductory Chemistry 




Chapter XI 167 

Fill the negative pole cup — the one with the lead wire — about half full 
of dilute sulphuric acid. Fill the other pole half full of a mixture pre- 
pared as follows: Dilute one part of concentrated hydrochloric acid with 
one part of water, and add a little chloride of lime: — enough chlorine 
should be evolved by the action of this mixture to saturate the liquid. 

Connect up the whole apparatus, turn on a moderate current, and allow 
it to run for a few minutes until it appears that the gases collect in the 
burettes at equal rates. Then interrupt the electric current, refill the 
burettes with water, and turn on the electric current again. Note the 
rates at which, the gases collect in the burettes. Repeat the measurement. 
How is the ratio of these volumes of hydrogen and chlorine, respectively, 
related to the ratio in which the gases combine by volume? 

Note, however, that in this electrolytic cell, the hydrogen is 
evolved from sulphuric acid, the chlorine from hydrochloric acid, 
and the ions transported between the poles are those of sodium 
chloride. The result would have been the same had hydrochloric 
acid been used in all compartments of the cell, but this arrange- 
ment serves incidentally to point out the independence of the 
three actions in a striking way. 



168 Schoch: Introductory Chemistry 



CHAPTER XII. 

BATTERY CELLS AND OXIDATION-REDUCTION REACTIONS. 

1. The Products of Electrolysis Are Electromotively Active Sub- 
stances. 

If an electrolytic cell has bad a current passing through it 
for a while, and then the wires connected to its poles are dis- 
connected from the source of electric current and connected with 
their loose ends to a voltmeter, the aeedle of the latter will deflect 
bo as to indicate that a current is flowing in the direction oppo- 
site to that of the previous electrolyzing current. As this cur- 
rent is allowed to flow, the electrolytic products present at the 
poles change hack to the original substances which they were be- 
fore electrolysis had begun,— or, in other word-, the pole reac- 
tions take place in a direction the reverse of that in which they 
took place during electrolysis. 

Experiment. — Secure the apparatus used in Experiment, Chapter XT. 
Article .'>, and connect a voltmeter (range, about :i volts) to the poles of 
tli i- cell before any current has been sent through it. The voltmeter 
should show practically no deflection, hut if it shows any deflection, its 
poles should he "short-circuited" a few minutes by connecting them di- 
rectly with a copper wire. When the voltmeter is applied again, prac- 
tically no deflection will lie observed. This Bhows that there are no sub- 
stances in the cell which tend to produce a continuous current. 

Xow connect the cell to the BOUrce of a direct electric current, and 
allow enough current to pass to deposit an appreciable amount of zinc, 
and evolve a noticeable amount of chlorine. Then apply the voltmeter 
again: it should register about 2 volts. 

The deflection of the voltmeter indicates that electrons are 
flowing through the wire and voltmeter from the zinc electrode 
to the chlorine electrode — i. e., in a direction opposite to that in 
which they flowed when zinc and chlorine were formed by elec- 
trolysis. With this new direction of flow of electrons, — the zinc 
and chlorine change back to zinc ions and chloride ions, respec- 
tively — i. e., the pole reactions now take place in a sense ex- 
pressed as follows : 

Zn°— > Zn + ^+?{— ) 

Cl 2 °+2(— ) — > 2C1-. 

Since no other force is acting in this circuit, it is evident that 
these substances must exert a tendency to change back to zinc 
ions and chloride ions, respectively, or at least, one of them must 
exert such a tendency with sufficient force to overcome any op- 
posing tendency of the other. The latter is the simplest view 
to take. According to this view, in a disconnected battery pole,, 
the materials react until the electrons produced exert a sufficient 



Chapter XII 169 

pressure to stop further change. Then when the two poles in a 
cell are connected the flow of electrons through the connecting 
wire will take place just like the flow of a gas through a pipe; 
that is, from the pole in which the electrons are under greater 
pressure to the pole in which they are under lesser pressure. 
Evidently, in the cell under consideration, the zinc pole is the 
one in which the pressure or concentration of electrons produced 
bv the reaction 

Zn°=Zn ++ +2(— ) 

is greater than the pressure or concentration of electrons in the 
chlorine pole produced by the reaction 

2Cl-=Cl 2 °+2(— ) 

As the electrons flow out of the zinc pole, zinc changes to zinc 
ions to replace the electrons which have flown out; and as the 
electrons flow into the chlorine electrode, chlorine changes to 
chloride ions to use up the electrons which have arrived. Fur- 
thermore, the electromotive force or voltage between the poles is 
directly dependent upon the difference between the electron pres- 
sures or concentrations in the two poles, and hence serves as a 
measure of this difference between the electron pressures. 

2. The Electromotive Tendency Possessed by Some Substances is 

Their Natural Property, and Does Not Depend on Their 
Methods of Preparation. 

In order to obtain a cell which tends to send out an electric 
current, we need merely to secure a cell arranged for electrol- 
ysis and place, in contact with their respective poles, some of 
each of the two materials that would be produced by electrolysis 
at the two poles; however, these materials need not have been 
obtained by electrolysis, but may have been prepared by any 
chemical process whatever. Thus, whenever zinc and chlorine 
from any sources whatever are placed in a cell arranged for the 
electrolysis of zinc chloride, the cell will always act to produce 
an electric current with the same voltage. This will be shown in 
the experiment below. Such an arrangement of material which 
tends to send out an electric current is called a battery cell. 

3. The Poles of Battery Cells Are Independent of Each Other in 

Their Behavior. 

Experiment. — (a) Secure five small porous "battery" cups, and fill 
them as follows: 

1. Fill with a solution of zinc sulphate and put in a rod of zinc or a 
clean strip of sheet zinc with a '"'wire connector." 

2. Fill with a solution of cadmium sulphate, and put in a rod or strip 
of sheet cadmium with a wire connector. 

3. Fill with a solution of, copper sulphate and insert a bright piece 
of sheet copper with a wire connector. 



1T0 Schoch: Ixteoductoey Chemistey 

4. Fill with dilute hydrochloric acid to -which has been added 2 . : 
grams of bleaching powder — i. e.. enough to saturate the solutio:. 
chlorine. Insert an electric arc carbon or a graphite rod with a copper 
connecting wire well '"twisted" on. 

5. Fill with a solution of iodine in potassium iodide, and insert a 
carbon rod as in Xo. 4. 

Secure a large beaker half filled with saturated sodium chloride solu- 
tion. Put the zinc pole cup into this beaker, and connect the zinc to the 
negative connector on a voltmeter (with a range of 3 volts or only 
slightly m 

Then insert, in turn, cups 2-5. connecting the poles, in turn, to the 
positive connector of the voltmeter. The voltages measured 
approximately as folio-- 

Cadmium against zinc. 0.36 volt. 
Copper against zinc. 1.10 volts. 
Iodine against zinc. 1.30 v 
Chlorine against zinc. 2.11 

w let us consider the zinc pole to be a "common refer 
pole,"'' and tabulate the voltages of all the cells formed by com- 
bining these poles in turn with this "reference pole." The 
age of the cell formed by combining the zinc pole with 
will natural]; ; and the others give the values obi 

above. Thus the following table will be obtained : 

Ha against Volts against 
zinc- 
Zinc pole 0.0 — •: 

Cadmium pole 0.36 —: 

Copper pole 1.10 —1.66 

Iodine pole 1.30 — 1 

Chlorine pole 2.11 —0.65 

Finally, let us subtract 2.T6 from each value and thus ol 
the voltages of cells formed by combining thee 
with a pole which combined with the zinc pole would give a cell 
with a voltage of 2.76 volts (with the zinc as the n _ 
These values are given in the last column of the table above. 
They are the same as the values in the large table bel 
this illustrates how the voltages in the large table were obtv 

If, in their behavior, the poles of battery cells are independent 
of each other, then the electric pressm - - m in each one by 
the reacting substance in it is always the same: and the vo> 
in the above table which show or "'measure" the difference- 
tween the electron pressure of the zinc pole and the other poles 
above, should give us, by simple subtraction, the voltage be~ - 
any other combination of these poles. This will now be shown 
to be true. 

Experiment. — (b The table shows that the voltage of the cell com- 
posed of a copper pole and a chlorine pole should be 1.0 volt, with the 
copper as the negative pole; that of the cell composed of the copper and 



Chapter XII 171 

of the cadmium pole should be 0.74 volt with cadmium as the negative 
pole. Verify these experimentally with the apparatus in the experiment 
above. What changes take place during action in the copper-chlorine 
cell? What changes in the copper-cadmium cell? Try the other com- 
binations possible and state how the pole materials change in them. 

4. The "Third Action" in Every Battery Cell. 

The two poles of a battery cell must be connected by a salt solu- 
tion for the same reason for which the poles of an electrolytic cell 
must be thus connected: — while the cell is sending a current 
through the wire from one pole to another, the reaction taking 
place at one pole will result in the temporary presence of an 
excess of cations over anions in that region, and the action at the 
other pole will result in an excess of anions over the cations in 
the latter region, and these two excesses are equalized by the 
double shift of ions throughout the solutions extending from pole 
to pole, as was pointed out in the study of electrolytic cells. 

5, A Table of Electromotive Reactions. 

By means of the same procedure as that employed with the 
five poles in the table above, all the common electromotively active 
substances have been tabulated, and thus the following table was 
obtained. The voltages given correspond to the electromotive 
forces of the cells that would be formed by combining the pole 
made from each substance, in turn, with the same positive pole. 
The latter has such an electron pressure that a cell formed by 
combining it with a zinc pole would have an e.m.f. of 2.76 volts; 
or combined with an acid-hydrogen pole (No. 17), an e.m.f. of 
2 volts. 

The substances in the left column tend to change to the corre- 
sponding substances in the right column with forces proportional 
to the numbers in the central column. The minus signs in 
front of these numbers may be ignored: — they are added merely 
to indicate that these poles act as negative poles when combined 
with the common reference pole to form battery cells. 



172 



Schoch: Introductory Chemistry 



TABLE OF ELECTROMOTIVE REACTIONS ARRANGED IN DESCENDING 

ORDER OF THE ELECTRIC PRESSURES PRODUCED THROUGH 

THEIR REACTION TENDENCIES. 



Elements in Reduced State 

(in Order of Decreasing Powers 

of Acting as Reducing 

Agents). •* 


Relation of 
Tendency 
to Change 
From Left 

to Right. 
Expressed 

in Volts. 


Elements in Oxidized State 
(in Order of Increasing 
Powers of Acting as Ox- 
idizing Agents, see 
Note 1 below). 




—5.00 
—4.80 
—4.50 
—3.50 
—3.00 
—2.80 

—2.76 

—2 

—2 i.; 

—2.40 
—2.35 

—2 . 3 1 

—2.17 
—2 . 1 5 

2. 12 

—2.10 
—2.0 

—1.8 (?) 

— 1 

— 1 70 

—1.66 
—1.46 

—1.25 

+ 120 
—1.14 
—1.12 

—0.92 
— 0.80(?) 

—0.65 
-0.7 to -0.50 

—0.49 (?) 

-0.80 to -0.30 

•7 

—0 . 30 (?) 

—0.34 

—0.10 
0.00 


Kt Salt solution +1 (— ) 






Ca+t Salt solution +2 (— ) 
Mg + + Salt solution +2 ( — ) 
Al + + t Salt solution +3 ( — ) 
II + ions in NaOH sol. (normal 

in OH") +1 (— ) 
Zn+t Salt solution +2 (— ) 
S° element +2 (— ) (See Note 

3) 
Fe + + Salt solution +2 ( — ) 










8 Sulphide ion (Sodium sulphide 
solution normal in S ) 




Cd + + Salt solution +2 ( — ) 


11 Sulphide ion (Sat. sol. of hydrogen 

sulphide in pure water) 

12 Lead metal (See Note | 


S° element +2 ( — ) (See Note 

3) 
Pb** in dil. TI 2 S0 4 +2 (— ) 

(Sat. sol. of PbSOj) 
Ni + + Salt solution -f2 ( — ) 


13 Nickel metal 


14 Sulphide ion (Sat, sol. of 1LS in 
normal HC1) 


S° element +2 (— ) 

Pb ++ Salt solution +2 ( — ) 


16 Tin metal 


(normal in Pb + + ; see also No. 
12 above and Note 3) 
Sn + + Salt solution +2 ( — ) 








mal solution of H + ion) 
Bi + + + Salt solution +3 < — I 


19 Stannous ion (stannous chloride 
solution) 


Sn+++ + Salt solution +2 (— ) 

(stannic chloride sol.) 
I Ig + Salt solution +1 ( — ) 


21 Copper metal 


(Hg 5 Cl 2 in normal CI sol.) 
Cu ++ Salt solution 4-2 ( — ) 


22 Iodide ion (normal in I~) 

23 Ferrous ion (Sol. normal in Fe + +) .... 

24 Silver metal 


1° element +1 (— ) (Sat. sol. 

of iodine) 
Fe+ ++ Salt solution +1 (— ) 

(normal in Fe +++ ) 
Ag + Salt solution +1 ( — ) 




Hgt Salt solution +1 ( — ) 


26 Oxygen ion (in NaOH Sol. normal 

in OH" ions) 

27 Bromide ion (sol. normal in Br ) 

28 Sulfur in compounds, with valence 

less than 6 ( +) (See Art. 22^ 

29 Chloride ion (sol. normal in Cl~) 


Oxygen gas (sat. sol.) +2 ( — ) 

Br° element (sat. sol ) +1 (— ) 
S 6t compounds -f- free ( — ) 

(cone. H 2 S0 4 ) 
Cl° element (sat. sol.) +1 ( — ) 
Cr e+ compounds + free ( — ) 




(Sol. of chromic acid) 
Mn' + compounds +5 ( — ) 


32 Nitrogen in compounds, with valence 

less than 5 ( +) (See Art. 14) 

33 Cl° element (See Art. 25) 


(Sol. of permanganate) 
N s+ compounds (HN0 3 ) +free 

(— ) 
Chlorine in compounds where it 


34 Oxygen ions fin any acid sol. having 

very few 0~~ ions) 

35 Pb+ + ion (in sat. sol. of PbS0 4 in 

dil. H„S0 4 (See Note 7) 


has positive valence + free 
(— ) (NaOCl, KCIO3 ' 

Oxygen gas liberated from a 
platinum pole by electrolysis 
of sols, of oxy-acids such as 
nitrates, sulphates, phos- 
phates + free ( — ) 

Pb* + (from Pb0 4 — solid in dil. 
H 2 S0 4 ) + free (— ) 




F° element + 1 ( — ) 




Theoretical zero pole 







Chapter XII 173 

6. Notes on the Table of Electromotive Reactions. 

Note 1. — The voltages in this table have been obtained by 
using poles in which all solutions have normal concentrations of 
the ingredients mentioned except where other concentrations are 
stated specially in the table. Since the reacting tendencies of 
substances vary with their concentrations, it follows that the 
tendencies to reaction will be different when the concentrations 
of the substances are different from those given here : — the volt- 
ages in the central column will be larger if the substances in the 
left column are employed in a more concentrated form than that 
here mentioned, — the voltages will be less if the substances on 
the right are present in a more concentrated form than that here 
mentioned. 

Note 2. — Metals Nos. 1-5 in left column react on contact with 
water (2K-|-2HOH— 2KOH-f-H 2 ), an d hence can be used to re- 
act with other substances only when water is absent. 

Note 3. — The relative tendencies to reaction indicated by the 
position of these substances in the table is not changed exten- 
sively by ordinary diluting or concentrating of the solutions; but 
with large differences in concentrations, such as the difference 
between the hydrogen ion concentration in an acid on one hand 
and in pure water on the other (the latter contains one-ten mil- 
lionth as much H ion as the former!), the voltage of the same 
material has largely different values. Only on this account do 
some materials appear at several different places in the table. 
Compare No. 6 with No. 17 and No. 8 with 11 and 14. 

Note 4. — See Note 3 and compare No. 12 with 15. 

Note 5. — The reaction for the change of bichromates in No. 
30 is— 

7H 2 0+2K + +2Cr + + + <— K 2 Cr 2 7 + 6 (— ) -f 14H + 

Note 6. — The equation for No. 31 is — 

4H 2 0+K + -f Mn + + *< — KMnO^+5 (— ) +8H + 

Note 7. — The equation for the change in No. 35 is — 

2H 2 0+PbSO i ±^Pb0 2 +2(— )+4H + +S0 4 -- 

Note 8. — Fluorine gas reacts on contact with water — 

(2F 2 +2H 2 0=2H 2 F,+0 2 ) 

and hence can be used to react with other substances only when 
water is absent. 

7. Exercise on the Table of Electromotive Reactions. 

A. To select the materials for any battery cell possible with 
the common substances, proceed as follows : Select any substance 



174 Schoch: Ixteoductoky Chemistry 

in the left-hand column for the negative pole — it will change to 
the corresponding substance in the right-hand column, if any~sub- 
stance in the right-hand column on a lower line is placed at the 
positive pole. The latter is forced to change to its corresponding 
substance in the left-hand column because the change of the first 
substance produces a greater electron pressure than the second can 
withstand. The voltage of the cell is equal to the voltage of the 
first change minus the voltage of the second change. 

1. The well known Daniell cell is made up by placing zinc 
(i. e., Xo. 7 left) at the negative pole, and copper sulphate (i. 
e., Xo. 21 right) at the positive pole. Its voltage is 2.76 — 1.66 
= 1.10 volts. Its pole reactions are: — 

Zn°=Zn ++ +2(— ) 

Cu- + +2(— ) = Cu° 

Make a list of other cells in which the same kind of change 
take place — of a free metal at the negative pole and of a metal 
ion at the positive pole. State their voltages and write their pole 
reactions. 

2. Write the pole reactions of a cell composed of Xo. 21 left 
and Xo. 29 right. What is the voltage of this cell? Make a list 
of other cells in which the same kind of changes take place — of 
an anion at the negative pole and of a free non-metal at the posi- 
tive pole. State their voltages and write their pole equations. 

3. Write the equation for Xo. 19 changing from the substance 
on the left to the substance on the right. Ditto for Xo. 23. 
Combine Xo. 19 right, and Xo. 23 right, each in turn, with Xo. 
7 left. State the voltages of the combinations and write the pole 
equations. 

B. For the actual construction of batten* cells, we must 
secure in general, a jar or beaker filled with a concentrated salt 
solution, and put into it two porous earthenware cups as in Ex- 
periment, Art. 3. Put into one cup all the materials named in 
both right and left columns of one of the horizontal lines selected 
for this cell from the table, and put into the other cup all the 
materials named in the other line. The metallic materials must 
be supplied in a shape which admits of connecting them to the 
conducting wire; in the absence of a metallic material in the 
pole, a rod of a chemically inactive material must be supplied to 
make the electrical connection (in general, a rod of graphite!). 
These changes and the electromotive forces will be exactly as in- 
ferred from the data in the table. An "outline" sketch of the 
cross-section of the battery cell thus assembled is shown in the 
accompanving figure? — (a) from lines 7 and 21, and (b) from 
lines 22 and 27." 

1. Make sketches similar to (a) of the battery cells obtained 
with 10 and 24, 15 and 21, 7 and 15. 



Chapter XII 



175 



- ^> 



a _ 



"Zinc Rod. 
Z/nc Sa/t' 
So/isf/on 




Cojb/ber Roc/. 

Cojbjber Sa/t 
So/uf/on* 



6roJb/?/fe Roc/: 
SoJvtton Cotjta/titt7jte+~ 

A/ and loc/tn e. 




Grahhite R.oc* 
**\- -5o/v//or? Contamtncf 
A/a C/ and Ch lor me 



1T6 



Schoch: Ixtbodcctoky Chbhstrt 



Make sketches sim il ar to (b) of the batterr cells obtained 
--:: ;.:_-:- •... iz. : •;:. - ■—: : .\. \' _:_\ \ ■ . 

3. Figure (c) is a diagram of the essential parts of the lead 
storage battery, which is built up from the materials mentioned 
in lines 12 and 35. Note that the poles contain all the materials 
mentioned in these lines. — that the liquid around both poles is 
the same, hence there i * no need of porous cups nor of another 
connecting solution. (See footno- 



SAe/efon of 
Lead 



fecAet Contain 
cmdPlSO /o~d. 




+ 
5Ae/e/<?/7 of 
Lead 

Pockets Con ta/n/n^ 

and Pb 30} fomdiu- 



The reactions of the 'Salenee-ehangers" in the poles of the 
storage batterr are: 

Pb = =y - 

an t~ 

Both of these reactions are immediately followed by the combin- 
ing of the Fb' * with S the complete change at 
the negative pole : ; — 

— . — 

t positiTe pole, the reaction is further accompanied by 
of the 2Q-~ ions from the PbO, combining with 4H- 



Hence the complete change at the positiTe pole 



I - — 



? — -:-: -— - — . — 



in its 



:■: 






Chapter XII 177 

C. It is shown at the opening of this chapter that the electrol- 
ysis of a solution of zinc chloride produced a battery cell with an 
electromotive force equal to the combined electromotive force of 
its products: zinc and chlorine. In order that the electrolyzing 
current may continue to flow, it must be impelled from without 
by a voltage or electromotive force large?' than the opposing volt- 
age of its products: zinc and chlorine. This opposing voltage or 
electromotive force of the products is called the back or counter 
electromotive force, and the value of this force in different ex- 
amples may be ascertained from the table, as follows : A solu- 
tion of zinc chloride is a solution of both chloride ions and zinc 
ions, or the material found in 29 left and 7 right. It is evi- 
dent that 29 left can change to 29 right only if the electrons pro- 
duced thereby will be taken away. This is done by an "electric 
pump" (i. e., a battery or dynamo), which, in this case, sends 
the electrons to the other pole, where 7 right is made to take up 
the electrons and change to 7 left. The "pump" must exert an 
e.m.f. larger than the difference between that in 7 and 29. 

1. Ascertain from the table, the back electromotive force which 
must be overcome by the applied e.m.f. when dilute hydrochloric 
acid is to be electrolyzed ; when zinc iodide solution is to be 
electrolyzed ; when cadmium bromide solution is to be electro- 
lyzed. 

2. Compare the voltage required to electrolyze HC1 solution 
with that required to electrolyze HBr solution. If the solution 
in an electrolytic cell contained both of these substances, and the 
voltage applied at the poles began with a zero value and were in- 
creased gradually until a continuous current first begins to flow, 
which one of the two anions present would be discharged? If 
HI were also in the solution, which anion would be discharged 
Avith the least e.m.f. applied to the cell? In general, what is 
the relative position in the table of the first of several anodic 
changes possible that would take place? 

3. Ascertain, from the table, the back electromotive force that 
must be overcome by the applied electromotive force when a solu- 
tion of copper sulphate is to be electrolyzed. Compare this with 
the back electromotive force in the electrolysis of zinc sulphate 
solution. State which metal would be the first one to be de- 
posited if a gradually increased voltage were applied to an elec- 
trolytic cell containing both of these salts. Which metal would 
thus be deposited first out of a solution of copper nitrate and sil- 
ver nitrate ? Which out of. a solution containing cadmium chlo- 
ride and mercuric chloride? In general, what is the relative po- 
sition in the table of the first of several cathodic changes possi- 
ble that would take place? 



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in CnO. Hence, wheneter Cn* is changed to 
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from Cn° to C~ 

or Ct to CL° 

indicate oridatifm^ Both of tliese particular changes inrotve the 

:- : — ■: — = :--- 

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in: i :r :•- :: r :_ -- _--:.t:.\". it.: ~1ht".-= ir±i:T::r ::: :r,.izz'.:~, 
is tins: — oxidation is anm change in which the tmlenee of am els- 
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; Z-e: 



~ r z zi~ ' : -z"- 1 :z -~'i -.~z\l-z.' -~~:-: ;; - ' :-:- ' : ~- 
mhich is tibe lover state of oxidation (or reduced state) ? 



Chapter XII 179 

a. Sulphur as S° or as H„S? 

b. Copper as CuS0 4 or as Cu° ? 

c. Iodine as KI or as I 2 ° ? 

d. Lead as Pb° or as Pb(N0 3 ) 2 ? 

e. Lead as PbSO, or as Pb0 2 ? 

2. Judging from the data in the Table of Electromotive Ke- 
actions, have the elements in the following form any tendency 
to change to more oxidized states, or are they in the highest state 
of oxidation, and hence can be changed only by being forced back 
to more reduced states? 

a. Copper in CuS0 4 ? 

b. Chlorine in HC1? 

c. Lead metal? 

d. Iodine element? 

e. Lead in PbO, ? 

f. Sulphur in H,S? 

g. Cadmium in CdCl 2 ? 
h. Chlorine gas? 

i. Hydrogen gas? 

10. The Two Pole Actions of a Battery Cell Constitute an Oxida- 
tion-Reduction Reaction; and Vice Versa. 

Experiment. — (a) Put some finely granulated zinc, or some zinc 
"dust" into a test-tube, add some copper sulphate solution, and shake the 
mixture until the blue color of the copper ion (?) has disappeared. Note 
the color of the metal formed. Pour some of the resulting liquid through 
a filter and into another test-tube, add a little ammonia and H 2 S water. 
The formation of a white precipitate (ZnS) shows that zinc has been 
dissolved; i. e., changed to a salt. 

The reaction in the mixture above is — 

Zn°4-CuS0 4 =ZnS0,+Cu° 

or Zn°+Cu ++ =:Zn ++ -f-Cu 

This reaction is evidently the sum of the two reactions — 

Zn°=Zn ++ -f2(— ) 

Cu ++ +2(— )=Cu° 

which are the two pole actions that take place in the cell formed 
by coupling of the copper pole (No. 21) with the zinc pole (No. 
7). This test-tube with zinc and copper solution contains all 
the parts necessary for the action of the cell, because in this 
cell only zinc and copper ions are changed. If we imagine the 
two poles and pole liquids in the preceding figure (a) brought 
together until the two porous cups become one and the poles 
touch, then no connecting wire is needed, the salt solution be- 
tween the cups also is unnecessary, and the cup contains just the 
materials in the test-tube above; hence the test-tube above con- 
tains all necessary parts of the whole cell, and the same forces 



"n: 



■-L, 




= Lv - . - - 



— i: :: ::- 



• : ~, 



1- 



li ■-!_• i :~ : i - 




nr! _ V _*i 



--- 




/. .- _- r_ :_:-: 



Chapter XII 181 

11. The Reaction of Battery Cell Constituents. 

It is evident from these examples that the acting materials in 
any battery cell will react if mixed together, — hence any material 
in the left column of the Table of Electromotive Reactions will 
react with any material in the right column below the line of the 
first material. This includes all the oxidation-reduction reactions 
possible between the common substances. 

In order to learn all the reactions possible, the student should 
learn the order of the. substances in the left column, and the kind 
of substance each one changes into (given in the right-hand col- 
umn, on the same line). 

Then he should drill himself by answering the following ques- 
tions, and make up and answer others like them. The substances 
in the upper part of the left column in the table should be re- 
membered as being strong reducing agents; those in the lower 
part of the right column as strong oxidizing agents. 

12. Exercise. 

1. Judging from the information given in the table, will cop- 
per metal react with a solution of a mercuric salt? Put a bright 
strip of copper into a small amount of mercury salt solution, and 
note the result obtained. What is reduced? What oxidized? 
Write the equation from the reaction. 

2. Recall the reaction between SnCl 2 and HgCl 2 ; in this 
change, which element is oxidized? Which reduced? 

3. Ascertain from your text what metals are frequently found 
in the earth in the form of free metals, — which rarely, — and 
which are never found as free metals : — relate your findings to 
the order of the metals in this table. 

4. What metals liberate hydrogen from acids? How must 
two metals be related in position in the table in order that one 
placed in a solution of a simple salt of the other will reduce the 
latter? 

5. How must the non-metals — oxygen, sulphur, chlorine, bro- 
mine, iodine — be related in position in the table in order that 
one mixed with a solution of a "salt" of the other will oxidize the 
latter? 

6. Will 11 left (or Ik left) react when mixed with 23 right? 
What is oxidized? What is reduced? Figure out the equation 
for the reaction. Locate this equation in the preceding part of 
this manual. 

13. The Complete Ionization of Ternary Compounds, e. g., HNO> 

H,S0 4 , Etc., Into Ions Composed of Single Elements. 

The primary ionization of NH,C1 yields NH 4 + and CI", but 
complete ionization into the elemental parts requires the further 
ionization of NH 4 + . Since 4H + result from this ionization, and 






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es npai; it foUorvs tint 3 (-) Euro 

\--"K Hue wbofe eonposrad in the $nm 
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v 



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Chapter XII 



183 



TABLE OF NITROGEN COMPOUNDS IN THE ORDER OF THEIR EXTENT 
OF REDUCTION FROM NITRIC ACID. 



Compounds. 


Elemental 
Ions from 
Theoretical 
Ionization. 


Amount of 

Reduction from 

HN0 3 : Electrons 

per 1 N. 


1 HN0 3 — Nitric Acid (and Nitrates) 


H\ N 5 + 30" 
N*+, 20" 
H + , N 3+ , 20" 
N++, 0" 
2N+, 0" 
N° 
N"\3H+ 





2 N0 2 Nitric Peroxide 


1 


3 HNO3 Nitrous Acid (and Nitrites).... 




4*. NO Nitric Oxide 


2 


5. N2O, Nitrous Oxide 


4 


6. N, Nitrogen 


5 


7. NH 3 (or NH 4 0H), Ammonia (or its salts) 


8 



The student should commit the foregoing table to memory. 

15. General Facts Concerning the Action of Nitric Acid with 
Various Reducing Agents. 

From the position of nitric acid in the Table of Electromotive 
Beactions, it is seen that nitric acid reacts with all substances in 
the left column above line 32, and this is certainly true of all 
substances beginning with 29 left. Technically, we say: — all 
these substances in the left column from 29 up are oxidized by 
nitric acid. In all such reactions, the nitric acid is reduced to 
its various products named in the table above. It is seldom that, 
in any case, only one particular reduction product is formed; 
however, under particular conditions some particular product is 
formed chiefly. The following general rule connects these con- 
ditions with the chief product formed in e?tch case: — the nitric 
acid is reduced to a greater extent if its solution is more dilute 
or if stronger reducing agents act upon it. For example — 

cone. HN0 3 -f-copper gives N0 2 
dil. HN0 3 +copper gives NO 
dil. HN0 3 + zmc gives 1ST 
very dil. HN0 3 -|-zinc gives KH 3 

The above rule and these examples should be committed to 
memory and used as a means of predicting the extents of reduc- 
tion of nitric in other mixtures. 



16. Nitric Acid Pole Reactions. 

The electromotive reactions for the formation of the six different 
reduction products of nitric acid are expressed by the following 
equations : 



" ; ^ loch: Ixteoductoey Oaaasna 

(H-. X : ~, 30"- -: — -1 extra H-=X~0.— E. 

H* X-- K " -; 1 a±n H*=mTO a 

W ' 10-- 3 extra H-=X0-2i: 

:: 4-2X4 . -tra H-=X - 

B(H* X'. 30---. " 8X5 ::ra H~=X : . 

- H : 

(H* X'. 30"- -Ufi B :::ra H-=XH,— 33' 

The equation? for the reactions between nitric acid and various 
redo - - _ ther with experiments 

in which these reactions take place. 

17. Demonstration of the Great Oxidizing Tendency of Concen- 
trated Nitric Acid. 

Experiment. — Secure a porcelain dish, about six or eight inches in 
diameter, and put into it some tap-water. Secure, in a test-tube, a few 
c.c. of fuming nitric and a small piece of charcoal. Hold the test-tube 
with a clamp, warm the nitric acid, and at the same time hold the 
charcoal, with a pair of the flame of a burner until it has 

d. Then, while holding the test-tube over the dish full of water 
I precaution agair. - p rop the glowing charcoal into 

it. The charcoal should burn vigorously in the acid. 

This shows that, at high temperatures. 1 nitric acid dissociates 
BO as i -m free oxygen. This it can do only by forming X — 
compounds in which X has a lesser valence than 5, as shown, for 
instance, by the equation: 

?HXO-=H 
X — valence X — valence 

=5 =4 

Since the X in HXO.. actually does this valence changing at high 
temperatures, if s i be expected that it exerts some of this 
tendency everi at ordinary temperate: 

•18. The Preparation of Nitric Peroxide. 

Experiment. — Pr.t a little "scrap" sheet copper into a test-tube and 
add about 1 c.c. of concentrated nitric acid to it. The reddish-brown gas 
evolved is nitric peroxide — NO* It is produced by the least reduction of 
nitric acid. Its production under these conditions is all that is to be 
noted here. 

7 his reaction between copper and concentrated nitric acid is 
evidently a combination of equation (a). Art. 16. 

(H-. X 5 -. 30- -^— 1 ( — )—] extra H"=XO £ — H_0. 



Chapter XII 185 

and of the electromotive change of copper, — 

Cu° = Cu + M-2(— ) 

In order that the electrons formed from Cu° will be taken up 
wholly by the HN0 3 , 2HN0 3 must change while 1 Cu° changes; 
hence we must multiply the first equation by 2 and obtain, — 

2HN0 3 -[-2 (— ) -f 2H + :==2JTO 2 +2H 2 

Then, taking the second equation, 

Cu° = Cu ++ -f2(— ) 

adding the left sides and the right sides, cancelling the electrons, 
and adding the extra N0 3 ions, we obtain the common form of 
the equation : 

2HN0,+lCu o +2HN0,-2N0 2 +2.H 2 0+lCu(N0 3 ) 2 

19. The Preparation and Some of the Properties of Nitric Oxide. 

Experiment. — Fit up a flask as for the preparation of hydrogen — with 
a two-hole rubber stopper, a delivery tube, and a thistle-top funnel, the 
stem of which extends to the bottom of the flask. Put into the flask 
about 10 grams of small pieces of sheet copper (scrap!), add about 15 
c.c. of water, and then when ready for all that is to follow (see below), 
add gradually an equal volume of concentrated nitric acid. Collect the 
gas evolved over water. This colorless gas is nitric oxide, NO: — it is only 
slightly soluble in water. Fill one wide-mouth bottle (about 500 c.c. 
capacity) wholly with the gas; but fill a second bottle only one-third full 
and leave this bottle in the water. Then let the gas bubble through a 
little of a solution of a ferrous salt (use ferrous-ammonium sulphate). 
The black compound, of ferrous ion and NO, is used as a means of reveal- 
ing the presence or absence of nitric acid in mixtures; i. e., in qualitative 
analysis. 

Lower a burning match into the bottle full of nitric oxide, — do this 
tfdth as little loss of the gas as possible. Then lower into the gas a 
deflagrating spoon with some well-burning red phosphorus. At low tem- 
peratures — such as those produced by the burning match even — the nitric 
oxide does not dissociate sufficiently to furnish oxygen of such concen- 
tration that the match may burn: — but at the higher temperature pro- 
duced by the burning of the phosphorus, the dissociation of nitric oxide 
furnishes oxygen of such concentration that the phosphorus may burn. 

The other bottle, which is filled only one-third full with nitric oxide, 
is to be tilted so as to admit some air: — note the formation of nitric 
peroxide which shows that nitric oxide and oxygen combine to form N0 2 . 
Then shake the bottle so as to splash the water up inside of it: — note 
that the reddish-brown fumes disappear — nitric peroxide dissolves in cold 
water, forming nitric acid and nitrous acid, according to the equation — 

2N0 2 4-H 2 0=HN0 2 +HN0 3 

Air may be admitted until all the nitric oxide has been used up. 

The reaction between dilute nitric acid and copper evidently 
consists of equation (c), Art. 16, and the equation for the change 
of copper. Here, HN"0 3 and Cu must change in the ratio 

2KN T <X : 3Cu° 



186 S koch: Introductory Chemistry 

in order that the electrons formed from the Cir may all be used 
up by the HXO ;r Multiplying the corresponding equations by 2 
and 3, we obtain — 

2HX0 3 -f-6 (— ) + 6H + =2NO+4H,0 
3Cu° =3Cu+++6(— ) 

Adding, cancelling the electrons, and adding the "inactive" X0 3 _ 
ions, we obtain — 

8HNO,+3Cii +6HNO t =2NO+4H 2 0+30u(NO t ) a 

20. The Reduction of Nitrates to Ammonia. 

Experiment. — Very strong reducing agents (zinc or aluminium) reduce 
very dilute nitric acid or nitrates to the extreme limit — ammonia. This 
is most conveniently accomplished as follows: — secure in a test-tube some 
finely divided aluminium, cover it with a concentrated solution of caustic 
soda, and add a few drops of dilute nitric acid: it will take a few minutes 
until a rigorous action has .set in. then the presence of ammonia will be 
noticeable. 

The equation for this reaction is the sum of equation (/) Art. 
16, and of the equation for the electromotive change of alumin- 
ium. From the numbers of electrons involved in these changes, it 
is evident that 3HN"0, eh le 8 (Al) change. Hence we 

multiply the first equation by 3. 

3HX0 3 +3X8(— )4-3XS extra H + =3XH 3 +9H 2 
and the second by S. thus : 

v\l = SAl--- — -2i( — ) 
On adding these, we obtain 

3HNO.+8A1+24 extra H*=3NH,+9H,0+8A1* + * 

get the final equation, we must add extra ions to change 
8A1--- to 8N&A10,. This requires 8Xa + ions, and 16 O - ions. 
These and also the 24 extra H~ ions in the equation above, will 
be supplied if we add SXaOH and 8H 2 0. Hence adding SXaOH 
and 8H\0 in place of the ?4 extra H+ and putting SXaA10 2 in 
place of 8A1 + + * we obtain the final form — 

3HNO,+8Al+8NaOH+8H 2 O=3NH 3 +8NaAlO 2 +9H 2 

In its simplest form, this equation is evidently, — 

3XaX0 3 +8Al-5XaOH-2H,0=3XH 3 +SXaA10 2 

21. Exercise on the Reduction Products of Nitric Acid. 

At the end of Art. 15 definite information was given regarding 
the reduction products of nitric acid of various concentrations 
with two representative metal-. Tt is often desired to write the 
equations for the reaction between a metal and nitric acid of a cer- 



Chapter XII 



187 



tain concentration. A list could be compiled of the reduction 
products obtained from all the metals — each with nitric acid of 
various concentrations. But such a list would be quite long and 
the student would not be able to remember it in its entirety. 
Hence the student should learn to make an "intelligent guess" as 
to the probable reduction product of nitric acid of any reaction. 
For this purpose, he should construct a table in the following way : 

(1) Divide the metals into three representative groups ac- 
cording to their position in the Electromotive Reaction Table in 
Art. 5, with zinc, lead, and copper as the representative metals of 
these groups. 

(2) Use three concentrations of nitric acid: concentrated, 
dilute, and very dilute nitric acid with each group of metals. 

(3) Use the data given at the end of Art. 15 to start the table. 

(4) Then, carefully fill out the table in the light of what has 
been learned so far in Arts. 14-20, inclusive. 



22. The Oxidizing Action of Sulphuric Acid. 

Concentrated sulphuric acid is a powerful oxidizing agent. It 
is used occasionally just like nitric acid to dissolve copper, sil- 



ver, or mercury, 



-l. e., 



metals which do not dissolve in hydro- 



chloric acid or in dilute sulphuric acid by liberating hydrogen 
gas: and, again like nitric acid, concentrated sulphuric acid does 
not attack gold or platinum. 

Since the main reduction products of sulphuric acid are known 
to the student, it is advisable to add here the few remarks neces- 
sary to inform him concerning the general facts involved in its 
oxidizing actions. 



THE COMPOUNDS OF SULPHUR IN DESCENDING ORDER OF OXIDATION 

STAGES. 



Order 


Common Form of Each 
Oxidation Stage 


Theoretical 
Elemental Ions 


Reduction 
Electrons per S 


1 


H 2 S0 4 , Concentrated Sulphuric Acid 
(and Sulphates) 


2H + , S 6+ 40 

S 4 *, 20"" 

S° 

2H + , S" ! 





2 


S0 2 , (or H 2 S0 3 ), Sulphur dioxide, sul- 
phurous acid, and sulphites 


2 


3 


S, Sulphur 


6 


4 


H 2 Si Hydrogen sulphide, and other sul- 
phides 


8 









Weak reducing agents, such as metallic silver, and metallic cop- 
per reduce concentrated sulphuric acid the least amount only — 
I. e., to S0 S . Strong reducing agents, such as zinc, reduce it to 
the greatest extent — i. e., to H 2 S. 



1813 - hoch: Ixtboductoet Cheaiistbt 

Experiment. — Put a ' ",eet copper into a test-tube, cover 

neentrated sulphuric acid, warm the mixture until reaction en- 
— note the odor of the escaping gas. Repeat this trial -with granu- 
lated zinc in place of copper. 

23. The Pole Reactions for Sulphuric Acid. 

The following equa: ~he reduction of H 2 S0 4 to 

reduction product- — 

?H-= SO --2H.0 

(i :: =s-f a 

: :> +fi h— h_>- 

The equation for the reaction between copper and sulphuric- 
acid is obtained by adding equation (a) above to the equation for 
the change of copper because lCu produces as many electr 

— H_>0", nan up to form SO.. The addition of - 
equations 

■fB^fi -■.H-=Cu----" .-■-::. 

Adding the inac: - we obtain — 

Cu-?H_S0 4 =rCuS0 4 -fS0,— -2H. 

obtain the equation for the reaction between Zn and H f S 
add together equation (c) above and — 

4-8 — 

94L The Reaction Between Concentrated Sulphuric Acid and the 
Three Ha Tides. 

: fact th sti _~er reducing agents reduce such oxidizing 
agents as concentrated sulphuric acid to a greater extent than 
weaker reducing agents is shown well by the action between con- 
centrated sulphuric acid and chlorides, bromides, and iodide - 

lively. It is evident from the position of the latter in the 
table of battery poles that their tendency to form the free hal 
increases in the order in which they are here named — chlorides, 
bromides, iodides — and in accordance with this we find that in 
the action of concentrated sulphuric acid with chlorides there is 
no oxidation or reduction, with bromides there is formation of 
bromine and slight reduction of the sulphuric acid (tc SO a — hile 
with iodides there is formation of iodine and very extensive re- 
duction of the sulphuric acid (to sulphur, or to hydrogen sulphide 
even). For a demonstration, try. in test-tubes, small amour: ; : 

ffiimn iodide and of potassium bromide, respectively, with a 
little concentrated sulphuric acid. The action be"—:: ::neen- 
trated sulphuric acid and chlorides may be remembered from 
earlier experiments. 



Chapter XII 



189 



With the data indicated in the foregoing, balance the equations 
which take place in these two test-tube trials. 

25. The Oxy-Halogen Compounds. 

The only compounds of the halogens dealt with so far in these 
oxidation-reduction reactions are the halides — which represent a 
lower oxidation stage than the free halogens. Besides these, there 
are other compounds of the halogens, such as chlorates and hypo- 
chlorites (bleaching powder!), in which the halogens exist in 
higher oxidation stages than that corresponding to the free halo- 
gen, and these are to be considered here. 



THE COMMON HALOGEN COMPOUNDS IN DESCENDING 
OXIDATION STAGES. 



ORDER OF 



(X stands for Cl, Br, or I.) 



Order 



Common Form of Each 
Oxidation Stage 



Theoretical 
Elemental Ion 



Reduction 
Electrons per X 



HX0 4 Perhalate (e. g. perchlorate, 
KC1 4 ) 

HXO, Halate (e. g. chlorate, KC1 3 ).. 

HXO, Halite (e. g. chlorite, KC1 O,) 

HXO, Hypo-halite (e. g. hypo-chlorite 
KCIO) 

Free halogen (e. g. Cl) 

HX, Halide (e. g. chloride, KC1) 



H+, X 7 *, 40" 
H*, X 6 +, 30" 
H+, X 3 +, 20" 

H+, X + , O 

X» 

Ht, X' 



The only oxy-halogen compounds which are of common occur- 
rence are the halates and the hypo-halites — more particularly the 
chlorates, and the hypo-chlorites. In the formation of these com- 
pounds, chlorine, bromine, and iodine are so nearly alike that it 
is necessary to illustrate with only one of these elements. 

The halates (e. g., KC10 3 ) are very stable salts, and strong 
oxidizing agents. Potassium chlorate is used in many cases where 
oxidizing agents are needed. In most of these reactions it is 
reduced to the chloride stage (6 electrons required per KC10 3 !). 
The hypo-halites (e. g., bleaching powder), are also strong oxidiz- 
ing agents, and on this account bleaching powder is one of the 
most valuable and widely used disinfectants for the purification 
of potable water, sterilization of sewage, etc. In such reactions, 
it is mostly reduced to the chloride stage (2 electrons necessary 
per NaClO). 



26. Fundamental Facts in the Behavior of Free Halogens and 
Hypohalites. 

(a) When a halogen is placed into pure water, a slight reac- 
tion takes place, yielding small quantities of hydrogen halide and 



190 Schc jel: Ixtboductobt Cttf^qstby 

the hypchalite acid, the principal part of the dissolved free halo- 
gen remaining in the solution as such. Illustrating with chlorine, 

the reaction is 

-H.O^ HCi-HCIO 

This reaction is a reversible reaction, which reaches equilibrium 
when most of the chlorine is in the form of CL C . If the solution 
is acidified, the equilibrium is shifted farther to thv L e., 

with the formation of more of the substances on the left-hand 
side of the equation above. These are observed facts. 

(b) When a halogen is placed into a solution of a strong 
base, the free halogen reacts almost completely to form the halide 
and the hypohalite, very little free halogen remaining in solu- 
tion as such. Illustrating again with chlorine, the reaction can 
be written 

T I ^T Xa< 1-XaClO-f H 2 0. 

again, is a reversible reaction with the equilibrium placed 
far to the "right" : of the chlorine is present in the 

form of compounds — the substances on the right of the equation 
above. This, again, is an observed f • 

What, then, is the fundamental difference in the nature of the 
two solutions (a and b) that causes this marked change in the 
point of equilibrium and in the quantities of halide and hypo- 
halite formed in the two cases? Consider the reaction (X rep- 
resenting a halog- 

X°»4-H»0 <y H--X--HX<:> 

The products of the equilibrium on the right are the H", the 
halide ion — X~, and the hypohalous acid — HXO. In solution 
there are a large number of H* io: ~ : in solution (b), 

there are extremely few H* ions present. The difference in be- 
havior of the two solutions, then, lies in the difference of the H~ 
ion concentrations, the equilibrium being "held" on the right by 
the X~. the H 1 by the hydrogen ions. If these H* ions 

are neutralized by the addition of OH" from a base, the equili- 
brium will shift toward the "right,'' causing the free halogen to 
disappear (as in b) : if the H^ ions are increased or not destr 
(as in a), the equilibrium will shift toward the "left/* Schemati- 
cally, this can be represented by the following tabular views: 

XX— H.O^: H— X-— HXO 

Fact: When the (H*) is 
small, then the (OH~) is 
large, and most of the halogen 

"•resent as X - and HX 



F": 


en : ; e X- is 


large, then the 


jH" := =r^X 


and most of t 


he halogen is in 



Chapter XII 191 

Conclusion: If free halogen is to be changed to halide and 
hypohalite, put the halogen into a basic solution (free OH~ 
present) ; and if hypohalite is to be changed to free halogen, make 
the hypohalite solution acidic (free H + ions present). 

Note: The hypohalous acids (hypochlorous, hypobroinous, and 
hypoiodous acids) are weak acids; i. e., they are only slightly 
ionized in solution. 

Experiment. — To one c.e. of sodium hydroxide solution add a few drops 
of bromine water and note how its color disappears (through the forma- 
tion of NaBr-f-NaBrO, which are colorless ! ) . 

The equation for the above reaction is 

Br 2 °+2NaOH=NaBr+]SraBrO+H 2 0. 

This reaction presents the novel feature of the same substance 
acting as the oxidizing and also as the reducing agent: 1 Br is 
oxidized to the Br + stage, and the other one is reduced to the Br" 
stage (ratio 1:1). In other words, the equation above is the sum 
of the following electromotive changes: 

Br 2 °=2Br + +2(— ) 
Bt 2 °+2(~)=2Bt- 
On addition: 2Br 2 °=2Br + +2Br- 
or Br 2 °=Br + +Br- 

Addition of one molecule of water gives the final form: 
Br 2 °+H 2 0=(H + , Br-)+HBrO. 

27. The Fundamental Facts Involved in the Formation of Halates. 

The formation of halates (of the general formula HXO. or 
MXO s ) from hypohalites depends upon the reaction of free hypo- 
halous acid with the hypohalite ion, (XO)~, from a salt of hypo- 
halous acid. This condition can exist only in a practically neu- 
tral or faintly acidic solution (or in the contact layer between 
acid and basic solutions!). The equation representing this 
change is 

2HX04-(XO)-=(X0 3 )-+2H + +2X- 

The condition imposed upon this reaction (i. e., almost neutral 
or faintly acidic solutions) can best be obtained: 

(a) by a solution of sodium bicarbonate acidified with car- 
bonic acid (a weak acid!), or 

(b) by a solution or suspension of Mg(OH) 2 or Ca(0H) 2 — 
very slightly soluble bases. 

The addition of a hypohalite to such a solution will produce a 
halate and a halide. A rise of temperature produces an increase 
in the velocity of reaction ; hence such solutions are heated. 

In actual practice, the free halogen is placed in a solution hav- 



- 
iialic 

-f B - 

sime elemoit 
tromt 

-H - 

- = 

- 

: 
vould be 

be 
4HCKH-Mg .= .. 

irodncei :Ations reacts 

roduce this chlorir- 

- 

ed jolntioii be- 

: 
sever: ibove: — 

- - -- - " 

Hie Oxidizi^i : H Acidified Permanganate Solution. 

A 



Chapter XII 193 

reacts — i. e., with all the substances above 30 left in the column 
of the Table of Electromotive Eeactions. The equation for the 
electromotive reaction of the acidified permanganate solution is 
given in Note 6, appended to the Table. 

The "key" to this electromotive change or "oxidizing action" 
of the permanganic acid is the fact that Mn 7+ (in HMnOJ 
changes to Mn 2+ (in MnS0 4 , MnCl 2 , etc.), or in symbols — 

Mn 7+ +5(— )=Mn 2+ 

Since Mn 7+ is accompanied by 1H + and 40~ " ions, we have — 

(H + , Mn 7 % 40")+5(— )+1 extra H + =:Mn 2+ +4H 2 

By combining this equation with the equations of the electro- 
motive changes of various "reducing agents" (e. g., FeS0 4 , or 
Zn°, or H 2 S, or HC1, etc.), the ordinary equations for the oxida- 
tion-reduction reactions of such mixtures are readily derived. 

Experiment. — Put a few c.c. of a solution of a permanganate into a 
test-tube, add 5 to 10 drops of dilute sulphuric acid, and add, drop by 
drop, a solution of a ferrous salt (e. g., FeS0 4 ) until the pink color of 
the permanganate has disappeared. The change of the color is due to the 
fact that the substances produced are relatively colorless. 

Repeat by adding SnCL, solution in place of ferrous sulphate solution. 

Repeat, passing hydrogen sulphide through the acidified permanganate 
solution instead of adding ferrous sulphate solution. 

Derive the equation for the changes in these mixtures. 

29. The Oxidizing Action of an Acidified Chromate Solution. 

A solution which contains a chromate and some free acid 
(H 2 S0 4 ) reacts with the same substances with which acidified 
permanganate solution reacts. The equation for the electromotive 
reaction is given in Note 5 to the Table of Electromotive Eeac- 
tions. The <f key" to this reaction is the fact that Cr 6+ (in 
H 2 Cr 2 7 ) changes to Cr 3f , or in symbols — 

Cr 6+ -!-3(— )=Cr 3+ 

Note 5 (appended to the Table) gives the complete equation 
for this electromotive change. Derive the ordinary equation for 
the oxidation-reduction reaction between this acidified bichro- 
mate and H 2 S. Also, pass H 2 S into hot solution containing 
H 2 S0 4 and a bichromate, and note the formation of free sul- 
phur, and the change of color from reddish-yellow to green: the 
latter is due to the change of chromium in chromates (Cr 6+ ) to 
chromium in chromic salts (Cr 3+ ). The latter are similar to 
aluminium salts and ferric salts. 



19-i - eeogh: Introductory Chemistky 

30. Keview Questions on Chapter XII. 

1. The Test for the nitrate ion is the reaction between FeS0 4 
and dilute HX0 3 . Figure out the complete equation for this re- 
action. 

2. When hydrogen sulphide is passed into an acidified solu- 
tion of potassium permanganate, the violet color of the perman- 
ganate disappears and the solution becomes milky. Write the 
equation for this reaction. 

3. A little sulphur dioxide is passed into clear hydrogen sul- 
phide water. The solution becomes milky. Write the complete 
equation. 

4. A solution of sodium iodide and sodium bromide is electro- 
lyzed. What are the products of electrolysis at each pole? Why? 

5. A solution of cadmium and nickel nitrates is subjected to 
electrolysis, the applied voltage beginning with zero value and is 
gradually increased to such a value that a metal begins to be de- 
posited. What metal will be deposited? Why? 

6. Concentrated sulphuric acid is poured on potassium iodide 
crystal- : the solution is turned reddish-violet. Write the equa- 
tion for the change that has taken place. 

T. Iron is added to a solution of silver nitrate. Describe what 
would happen and write the equation for the change. 

8. To an acidified solution of hydrogen sulphide some orange- 
colored potassium dichromate is added. The solution turns green. 
Write the equation for the reaction. 



Chapter XIII 195 



CHAPTER XIII. 

THE FUNDAMENTAL PRINCIPLES OF ORGANIC CHEMISTRY 
AND THE CHIEF TYPES OF ORGANIC COMPOUNDS. 

1. The Two Great Classes of Organic Compounds. 

Organic chemistry is the chemistry of the carbon compounds 
and is concerned with combinations of carbon with hydrogen, 
oxygen, nitrogen, sulphur, phosphorus, and the halogens. 

On account of important differences in properties, all organic 
compounds are divided into two great classes : the "straight-chain" 
or fatty compounds, and the "cyclic" or aromatic compounds. 
The former class includes among other substances the hydro- 
carbons found in petroleum, the sugars, oils and fats of animal 
and vegetable origin, etc., and the latter includes the "coal tar" 
dyes, carbolic acid, naphthalene, i. e., compounds obtained from 
coal tar or from coal tar distillates. The straight-chain com- 
pounds will be presented first, and we will begin with the simplest 
straight-chain compounds, the saturated hydrocarbons, or the 
paraffin series of hydrocarbons. They are also called the Methane 
or Marsh Gas series from the lowest member of the series, which 
is CH 4 , Methane or Marsh Gas. 

2. The Fundamental Ideas Underlying the Structure Theory of 

Compounds. 

Organic chemistry owes its wonderful development to the struc- 
ture theory, according to which the atoms in organic compounds 
are tied together by bonds, which in number are equal to the 
valences of the elements. The special fundamental ideas em- 
ployed in the structure of carbon compounds are these: 

1. The carbon atom always has a valence of 4. 

2. A carbon atom may be united to another carbon atom, and 
this in turn to another and so on without limit. 

3. Two carbon atoms may be directly connected by one, two 
or even three bonds. 

In accordance with these fundamental ideas, the structure of 
the hydrocarbons of the marsh gas series is represented as follows r 

H 

I 
Methane, CH t H— C— H 

I 
H 

H H 

i I 
Ethane, a.H 6 H— C— C— H 

I ! 

H H 



196 SCHOCH: IXTBODUCTOBY Chzmistey 

H H H 
Propane, C 6 H« H— C- 




Xote ( 1 ) that in every instance there are four lines, which rep- 
resent bonds, or valences, extending out from each I : (2 that 
in molecules having more than one C, the Cs are directlv united 
by bonds. 

Since H has one bond only, it is impossible to connect the atoms 
in the above molecules in any other manner than that shown and 
still give each carbon four valen. 

However, in the following compounds there are several different 
structural representations possible. Thus with 4 H ltJ we have 
either 

H H H H 

I I I I 
H— C— C-« — ( — H 

H H H H 
or 

H H H 

I ! 

H— C— C— C— H 



H H 

H— C— H 



This theoretical prediction of the existence of two different com- 
pounds, both of which have the composition C 4 H 10 agrees with the 
fact that two such compounds are actually known, and only two 
are known. They have the same composition but different prop- 
erties. 

An inspection of- the above formulae reveals that the Marsh 
gas or open-chain compounds obey the general series formula 
CnH2n— 2. The table below lists the boiling points of a few of 
this series, in all of which the C's are all in a straight chain: 
Methane CH 4 — 164°C 

Ethane OH, — : 

Propane H\ — 3T.0 

Butane CJL- +1.0 

Pentane C\E +35.0 

Hexane C.H M +71.0 

Heptane C T H ie ■ —99.0 

Hexadecane O w H M — vf M 



Chapter XIII 197 

It becomes evident from the above table that as the number of 
carbons in the molecule increases, the boiling point rises. The 
first four are gases at room temperature; the members from pen- 
tane to hexadecane are liquids; while the members starting with 
hexadecane are solids. 

3. Exercise. 

Figure out in the manner outlined in the preceding article all 
possible compounds of the formula C 5 H 12 differing in structure. 
Ditto for C 6 H 14 . 

4. Chief Property of the Paraffins: Inactivity. 

The name paraffin, is derived from the French and means "no 
affinity/' and it was given to the hydrocarbons of the paraffin series 
to indicate their chief characteristics. They react with very few 
reagents, and generally only slowly with any reagents. They are 
also called saturated hydrocarbons, because they do not unite di- 
rectly with any substance (see unsaturated hydrocarbons). Their 
marked chemical indifference, or stability, or non-reactivity, makes 
them specially useful wherever such a property is desired, as in the 
lubrication of bearings and in the oil wiping of machinery, for 
either of which purposes vegetable oils are utterly unsuitable. 
Paraffin is frequently melted into wood and into stone and cement 
to protect them against moisture (water proofing) and chemical 
agencies. Thus limestone has been protected in smoky cities 
(Pittsburgh) against the sulphuric acid formed from the sulphur 
in the coal. The obelisk known as Cleopatra's Needle, in Central 
Park, ~New York, has been protected by impregnation with paraffin, 
and plaster of Paris casts are thus made water proof. In the 
latter case the objects are painted with a solution of paraffin in 
benzine or gasoline. 

5. The Distillation of Crude Petroleum. 

In order to become acquainted with the commercial preparation 
and the common properties of some of these compounds, distill 
some crude petroleum as follows: 

Secure a distilling flask of about 250 c.c. capacity. Fit it with a 
360-degree thermometer, and with a wide piece of glass tubing for an 
"air" cooled condenser ( see figure ) . Secure a piece of asbestos board 6x6 
inches and cut a hole in the center 2 inches in diameter. Place this 
on the ring of a ring stand, clamp the flask to the ring stand, grasping 
the flask at the uppermost part of the neck, put any suitable object under 
the condenser tube for its support, and allow its delivery end to extend 
into a small flask. If a clamp is used to hold the condenser tube, as in 
the figure, then wads of folded paper should be placed between the jaws 
of the clamp and the glass tube. 

Begin by heating the oil cautiously. If water is present, the upper 






X K : INTRODUCTORY C 



HEMISTBT 




a 



Chapter XIII 



199 



part of the flask may have to be heated at the same time by a separate 
flame in order that the water will not condense there. The condenser 
tube should be placed at such an angle that the condensed liquids will 
run out quickly. When the temperature has reached 200 degrees, change 
the receiver and collect the portion coming over between 200 and 300 
degrees in a clean, dry flask. Note the color of the distillates; note the 
color and contrast it with that of the crude oil. The distillates obtained 
by two or three students should be poured together to get enough to make 
a specific gravity determination. If the amount of distillate is too small 
to use a "hydrometer," then a specific gravity balance should be employed. 
What is the specific gravity of this distillate? How does it compare 
with that of the original oil? 



6. Experiment on the Refining of Kerosene. 

Each student should then take his portion of the distillate and pro- 
ceed with it as follows: 

(a) Removal^ of Sulphur: Put a few c.c. of the distillate into a dry 
test-tube, add a 'little yellow lead oxide, and heat the mixture. A black- 
ening of the solid powder shows the formation of lead sulphide. Sulphur 
in kerosene, etc., is objectionable because it burns to sulphur dioxide, and 
is eventually oxidized to sulphuric acid in the air. Commercially, the 
sulphur is removed by treating the distillate with copper oxide or lead 
oxide, and then redistilling it. 

(b) Removal of Unsaturated Hydrocarbons: Put the remainder of 
the distillate into a dry flask, add one-fifth of its volume of concen- 
trated sulphuric acid, and shake the mixture vigorously. Set it aside 
until the two portions have separated thoroughly, decant the supernatant 
liquid into another flask, add distilled water, shake and then decant the 
oil as completely as possible from the water. Add next some concen- 
trated sodium hydroxide solution, using of it about 5 to 10 per cent of 
the volume of the oil. Shake as with the sulphuric acid, decant and 
wash with water as before. The resulting oil should be clear, colorless 
and of a sweet odor. This treatment removes the tarry matter which 
colors the oil, and also the small amount of ill-smelling compounds 
present. Clean all vessels by rinsing them out repeatedly with small 
quantities of gasoline, and either wiping them dry finally or allowing 
them to drain until perfectly dry. Reserve a small quantity of the re- 
fined oil for use in the experiment below. 

The distillates obtained below 300° C. can be separated into 
several quite distinct portions by a more careful fractional dis- 
tillation. The products obtained are given below, together with 
their most probable composition. 



Name. 


Constituents. 


B. P. (760mm.) 


Use. 


Petrolic Ether 




30°- 70°C. 

70°- 90° 

90°-120° 

120°-150° 

150°-300° 




Gasoline 


hexane and heptane 


fuel 


Naphtha 




Benzine 



















The distillates obtained from crude petroleum above 300 degrees 
are heavier and thicker than kerosene, and are called lubricating 
oils. The lightest of these are called "spindle oils/' the middle 
grades "machinery oils," and the heaviest "cylinder oils." 



200 Schoch: Introductory Chemistry 

At still higher temperatures, vaseline (C 19 H 40 to C 21 H 44 ) is 
obtained. When paraffin is present in the crude oil. it is extracted 
from the lubricating oil and vaseline oil distillates by chilling 
these: the solid paraffin separates (crystallizes out) and is filtered 
off. Crude oils which furnish paraffin are said to have a "paraffin 
base.'' In Texas, the Corsicana oils, the Thrall oils, and the 
Electra Field oils have a paraffin base, but the Beaumont oils have 
an "asphalt'*' base, and they yield no paraffin. The Kanger and 
Burkburnett oils have a mixed base, yielding both paraffin and 
asphalt, the ratio of paraffin to asphalt being about 60 to 40. As- 
phalt is a non-crystallizing, pitchy, or gum-like substance in the 
oil, which remains in the still until it is completely destroyed, 
leaving a solid carbon residue. If the distillation is discontinued 
at 300 degrees C. or slightly above, the residue from asphaltic oils 
forme an excellent binding material for road-building. Its value 
as a road-building material depends upon the per cent of binder 
or asphalt in it. and this is "measured*' in a sense by a "pulling" 
test. In Texas, many refineries do not distill beyond 300 decrees 
C, and sell the residue for fuel oil. 

7. A Test for Lubricating Oils: Viscosity. 

A lubricating oil is valuable on account of its property to form 
and maintain a film of oil between the two surfaces in contact. A 
light oil. with little "'body," is rapidly squeezed out by heavy bear- 
ings, and hence does not prevent friction. The less easily an oil 
flows, the less easily will it be squeezed out; hence, a measure of 
the usefulness of a lubricating oil for any definite purpose is the 
determination of its viscosity at the temperature at which it is 
to be used. The method is outlined below: 

Take a 25 c.e. or 50 e.c. pipette, and by means of a gummed label 
mark a point on the stem just below the bulb. Then fill the pipette with 
water, and note the time required for the pipette to empty from the 
mark above the bulb to the mark below the bulb. Dry the pipette by 
warming it above a flame and sucking air through it. Then determine 
the time required for an oil sample to flow out of this pipette. This 
period of time, divided by the time required for water to flow out. gives 
the viscosity. Secure a sample of lubricating oil and measure the viscos- 
ity. Then clean the pipette. 

8. Flash Point. 

In former years kerosene had to be examined for its flash point, 
because there was very little sale for gasoline, and hence as much 
of this as possible was left in the kerosene. At present there is 
.practically no danger from this source, because gasoline is more 
valuable than kerosene. The flash points of kerosene found in 
the Texas markets at present vary from 84 degrees F. to 102 de- 
grees F. In Texas a "minimum" flash point of kerosene is not 
fixed bv law. 



Chapter XIII 201 

Secure a small evaporating dish about 3* inches in diameter, and a 
second one a little larger. Put some sand into the larger one, and fit the 
smaller one within it, so that the two are separated everywhere by a layer 
of sand. Place these two dishes on the asbestos board with a 1 1-inch hole 
in it, fill the inner dish with a thin lubricating oil, and suspend a ther- 
mometer so that the bulb of the thermometer is immersed in the oil. 
Heat the oil with an adjustable flame so that the temperature rises uni- 
formly a few degrees (2-4) per minute. By means of another burner 
apply a very small flame to the surface of the oil once every minute. T^he 
temperature with which a flame first flashes across the surface of the oil 
without continuing to burn is the flash point. At a slightly higher tem- 
perature the flame will continue to burn; this is the burning point. 

The term gasoline is somewhat indefinite as to its composition. 
The ever increasing demand for gasoline for motor purposes nat- 
urally leads producers to include as much of the kerosene fraction 
with the gasoline as possible, and the gasoline has consequently 
become of poorer quality for a number of years. In order to 
check the indiscriminate addition of higher boiling fractions, the 
Thirty-sixth Legislature of Texas passed the following law (Sen- 
ate Bill 212), of which the two sections dealing with specifications 
are included: 

"Section 6. For the purpose of this act the word gasoline 
whether used alone or in connection with other words shall apply 
only to the petroleum products comptying with the following mini- 
mum requirements: 

(a) Boiling point must not be higher than 60° C. (140° F.). 

(b) Twenty per cent of the sample must distill below 105° C. 
(221° F.). 

(c) Forty-five per cent must distill below 135° C. (275° F.). 

(d) Mnety per cent must distill below 180° C. (336° F.). 

(e) The end or drv point of distillation must not be higher 
than 220° C. (428° F.). 

(f) Not less than ninety-five per cent of the liquid will be 
recovered from the distillation. 

(g) Gasoline is to be of high grade, refined and free from 
water and all impurities, and it shall have a vapor tension not 
greater than 10 pounds per square inch at 100 degrees Fahrenheit 
temperature. 

"Section 7. The apparatus and methods of conducting all tests 
and arriving at proper standards of gasoline and other products 
under this act shall be those now or herafter authorized and used 
by the U. S. Bureau of Mines." 

Ordinary gasoline on the market has a specific gravity of 64 to 
68 degrees Beaume (which corresponds to specific gravity of 0.721 
to 0.707). If the official tests for gasoline cannot be conven- 
iently made, it is well to test the specific gravity, for the heavier 
gasolines are, in general, less valuable. 

Note. — The Beaume specific gravity scale, although very un- 
scientific, is used so much in commerce that a word of explanation 



:>ch: Lsttbodcctoey Chemistby 

will not be out of place here. There are two distinct scales: one 
for liquids heavier than water and another for liquids lighter than 
water. The first was designed bj dissolving 15 parts of salt in 
urte of water at 12.5 degrees C. The point to which the 
spindle sinks in this solution is marked 15 degrees Be., and the 
point to which it sinks in water is marked degrees Be. The scale 
for liquids lighter than water is designed thus : Ten parts of salt 
ir~ ::--:>•?•: ;: ;'■: : it:.- :: -..:-.-:. m 1 ::.- ~- r.r. ::»->_;.;-. -":.-: .-_:.- 
die sinks in this is marked degrees Be., while the point to which 
dIdb in pure water is marked 10 degrees Be. Hence on this 
latter scale the number of degrees increases as the specific gravity 
decreases, while on the scale for liquids heavier than water the 
number of degrees increases as the specific gravity increo- 

In order to facilitate the conversion of Beaume readings into 
specific gravity readings, the following formula? are used: 

For h<arg liquids: Sp. Gr. =145-^ (145— deg., E 
I r light liquids: - = 1 H-(1304-d^_ 

9. Unsaturated Hydrocarbons. 

Tk~ ■ member of the paraffin series has the composition 

. and it has the characteristic property of the paraf ..- — 
namely, of being comparatively non-reactive. There is another 
two-C compound which occurs in illuminating gas, but which 
has the composition of C*H 4 and is called ethylene- In order to 
represent its structure in accordance with the idea that carbon is 
always tetravalent. we write — 

H— = — H 

H H 
reactive. Thus it combines very quickly with bromine 
to form a compound of the composition C JELJ$t~ More bromine 
than corresponds to this formula is not taken up readily. In 
order to express the structure of this compound, we write — 

H H 

Br Br 

On comparing this with the structural formula of C.JI 4 we note 
that the second bond between the Cs has been broken and the 
two Br*s have been attached by means of the bonds thus made 

Another two-C compound, which is well known in dairy life, 
has the formula C JL — acetylene. Its structures must be written 

:'.-: — 



Chapter XIII 203 

in order to represent carbon as tetravalent. This substance takes 
up bromine or chlorine and many other reagents very readily. 
With bromine it forms a compound of the formula C 2 H 2 Br 4 , but 
more bromine than corresponds to this formula is not taken up. 
That 4Br is the maximum amount that can be taken up is ren- 
dered plausible by writing the structure of this compound thus — 

H H 

I i 

Br— C-C— Br 

I ! 

Br Br 

which shows that it has a structure similar to the inactive com- 
pounds of the paraffin series. 

Compounds which like the C 2 H 4 and the C 2 H 2 above combine 
readily and direct with other substances are called unsaturated 
compounds: they always have either a double or triple bond in 
their structural formula. But substances similar to the paraffins 
in structure do not combine with other substances, and they are 
hence called saturated compounds. The C's in saturated com- 
pounds are connected by single bonds only, in their structural 
formulae. 

10. An Illustration of the Reactivity of Unsaturated Compounds. 

The marked tendency of unsaturated compounds to form "ad- 
dition compounds" can be readily demonstrated as follows: 

Secure some bromine water; then drop a fragment of calcium carbide 
into a little distilled water, and pour some of the water, thus saturated 
with acetylene, into the bromine water, until the color of the bromine 
has disappeared. Acetylene combines with bromine to form C 2 H 2 Br 4 . 
Note how rapidly the reaction takes place. Write the structural formula 
of this resulting compound. 

Acetylene can be burned without the formation of soot if it 
issues from a very fine opening. Great care must be exercised in 
handling the gas, because with copper compounds such as may be 
formed on brass fittings it forms a very explosive carbide, and 
mixed with air in any proportion it forms a very violently explod- 
ing mixture. (The latter is not true of the other common com- 
bustible gases : their mixture with air are not explosive if either 
ingredient is present in small amounts.) For the above reason, 
the use of tanks full of compressed acetylene gas cannot be safely 
used for lighting purposes. But the gas may be compressed into 
acetone, in which liquid it is very soluble. This liquid does not 
dissolve air or oxygen appreciably and hence contains no explosive 
mixture. Tanks full of this solution, called "Prestolite," were 
formerly used extensively for lighting purposes on automobiles, 
and are still used in the lighting of country homes. The prin- 



204 Schoch: Ixteoductoey Chemistry 

cipal use today, however, lies in its application in the welding and 
cutting of iron and steel. When acetylene is burned with oxygen 
in an oxy-acetylene torch, the temperature of the flame is ex- 
tremely high and will melt its way through a steel plate several 
feet wide or through a six-inch steel shaft in a very short while. 
A great deal of the repairing of broken steel castings is doue 
today by means of the oxy-acetylene torch. 

11. Alcohols. 

The term alcohol is a general one which denotes compounds in 
which an OH group is attached to a carbon atom with one bond 
while the other three bonds of this carbon atom are connected to 
other carbon atoms or to hydrogen atoms. Whenever a compound 
has this grouping — 

— C— 0— H 

I 
with the three bonds ''which are here left open" connected to 
H or to C atoms, then it is an alcohol. Thus the structure of 
the simplest alcohol in existence, wood alcohol, or methyl alcohol, 
is written as follows : 

H 

I 
H— C— 0— H 

I 

H 
and the compound of the structure — 

H H 
I | 
H— C— C— 0— H 

I I 
H H 

is also an alcohol (vinous alcohol or ethyl alcohol) because the 
carbon on the right in the figure shows the characteristic alcohol 
group. This ,sroup can occur on more than one carbon in the 
compound. Thus glycol (CH ? OH) 2 has the structure — 

H 

| 

H— C— 0— H 

I 
H—C-0— H 

! 
H 

and it is chemically ju^t as much an alcohol as the substances 
lust mentioned above. The same is true of glycerine, 



Chapter XIII 205 

H 2 C— 0— H 
H— C— 0— H 



H 2 C— 0— H 



Note the condensed form of the structural formula here given: 
from now on structural formulae will be written in as condensed 
a form as is compatible with clearness. 

The monovalent radicals (CH 3 , C 2 H 5 , C 3 H 7 ) obtained by taking 
away one H from the paraffin hydrocarbons (CH 4 , C 2 H 6 , C 3 H 8 ) 
are named by putting "yl" in place of "ane" in the name of the 
original hydrocarbon — e. g. : 

Methyl, CH 3 , is named from methane, CH 4 ; 

Ethyl, C 2 H 5 , is named from ethane, C 2 H 6 . 

The general term for such a radical is alkyl. 

12. The Connection Between Hydrocarbons and Alcohols. 

Theoretically the alcohols are the first derivatives obtainable by 
oxidizing hydrocarbons, but it is practically impossible to make 
alcohols this way. 

For scientific purposes, alcohols have been made direct from 
hydrocarbons, but the process is too expensive to be used com- 
mercially. However, this manner of formation of alcohols — di- 
rect from their hydrocarbon — is the means by which the structure 
of the alcohols was recognized — in a manner shown in the fol- 
lowing example: by treating methane, CH 4 , with chlorine under 
suitable conditions, a compound of the formula — 

H 

I 
H— C— CI 

i 
i 

H 

is obtained according to the equation : — 

CH 4 +C1 2 -H>- CH 3 C1+HC1 

and if this is treated with moist silver oxide (which may be con- 
sidered to be AgOH), then by metathetical reaction OH is put 
in place of CI, and hence the resulting compound should have the 
structure — 

H 

I 
H— C— 0— H 

I 
H 

The compound thus obtained is identical with the compound ob- 



9 hoch: Ixtroductoby -tby 

tained from the dry distillation of wood, and which is known as 
wood alcohol, or methyl alcohoL By means of the above scien- 
tific preparation of the various alcohols from hydrocarbons, the 
formulae and struct!" the alcohols have been thoroughly 

proven, and on account of this theoretical relation to the hydro- 
carbons the alcohols are here considered next in order: however, 
it should be noted that in their commercial preparation there is 
no direct connection between the hydrocarbons and the alcohols. 

13. Properties of Wood Alcohol (or Methyl Alcohol). 

:imercial methyl alcohol is often slightly yellowish in color, 
and has generally a disagreeable odor. Taken internally, i: 
as a poison, which, according to its concentration or the quantity 
taken, will produ headaches and nausea, or death, 

ounces taken internally in any form are said to produce either 
death or permanent blindness in most instances. Even its vapor 
produces these baneful results, particularly blindness, and hence 
K in industry, s a f r lacquers or varnishes, and for 

other to be deprecated, and the use of vinous alcohol to be 

advanced. When pure it boils at 66.7 degrees C. and has a specific 
gravr >95 at 15 deg It is perfectly miscible with 

water, vinous alcohol, and ether; and it is an excellent solve:. 

:.s, and is hence used in varnish making. It is also 
used as a fuel, and in some cases it is used as a denaturant of 
vinous alcohol, and it if to make formalin. 

14. The Preparation of Ethyl Alcohol by Fermentation. 

Secure about 30 grams of glucose or of some cheap molasses, dissolve 
it in about 150 c.c. of water, add some yeast, shake the mixture thor- 
oughly and warm it slightly I not abov? - Put the mixture into a 
flask. "leave this uncorked, and set it aside in your desk for two or three 
days, or until the slow evolution of a gas which takes place at first has 
practically ceased. Test for the presence of ethyl alcohol by means of 
the following test. 

15. The Iodoform Test for Ethyl Alcohol. 

A qualitative test for ethyl alcohol is made as follows: Warm a little 
of the solution to be examined, add a few iodine crystals and then add 
enough sodium hydroxide solution to decolorize the mixture. After the 
lapse of a short while, a yellow precipitate of iodoform ( CHI, > will ap- 
pear if alcohol is present in the sample. 

The reaction may be considered to take place as follows : 
CH..0H— 8I+OH HCOOH+ I HI 

= 

CH: - 61— H CHL — 3 HI 

or C 2 H,0H— >I-H,0=CHI,— 5HI— HCOOH 

:n place of HI and formic acid, their Xa salts are 



Chapter XIII 207 

obtained. This action is essentially an oxidation due to the oxi- 
dizing action of the iodine. 

Note. — Chloroform is made in the same way, from alcohol, by 
means of free chlorine gas : the latter is frequently added in the 
form of chlorinated lime (chloride of lime). 

16. The Determination of the Percentage of Ethyl Alcohol in a 

Liquid. 

The determination of the per cent of alcohol in liquids con- 
taining also materials other than alcohol is accomplished by dis- 
tilling the alcohol out of the liquid, determining the specific grav- 
ity of the distillate, and calculating the per cent of alcohol from 
the data obtained in this connection. 

Experiment. — Secure a 200 c.c. distilling flask and a 2 ft. Liebig con- 
denser, and mount the apparatus in the same way as shown in the figure 
with Art. 8 in this chapter. Hang the empty flask on a sensitive bal- 
ance, weigh it and put into the flask exactly 100 grams of the liquid 
obtained in Art. 14. Accurately weigh a 200 c.c. flask to be used as a 
receiver, and distill at the rate of 2 drops per second until about 40 c.c. 
have been collected in the receiver. Then add enough distilled water to 
bring the total weight of the liquid in the receiver to 50 grams. Take 
the specific gravity of this liquid with a plummet and balance, and note 
its temperature. With this data, look up, in a table, the per cent of 
alcohol in the distillate, and divide this by 2 to obtain the per cent in 
the original sample. 

17. Descriptive Data on Ethyl Alcohol. 

Alcohol and water cannot be completely separated by distilla- 
tion: at least 4 per cent of water will remain; hence the best com- 
mercial alcohol contains about 95 per cent of pure alcohol. The 
last traces of water can be removed by dehydrating agents only. 

Ethyl alcohol is one of the most important substances used in 
industry; e. g., as a solvent for gums and resins in making var- 
nishes, lacquers, etc. The amount needed for this purpose is al- 
most inconceivably large. Since it is the least poisonous of all 
alcohols, its place cannot — should not — be taken by others. The 
cost of production of this alcohol can possibly be so low that 
alcohol may even be considered as a possible rival of gasoline for 
internal combustion engines, and as a rival of kerosene for cook- 
ing stoves and for lamps. Alcohol has a decided advantage over 
kerosene and gasoline because its use as a fuel is attended with 
less danger and it forms no soot or odor. It can be produced 
profitably from cheap or refuse grain, potatoes, and even from 
sawdust. The "Denatured Alcohol Law" passed on June 7, 1906, 
made it possible to put this material on the market without the 
payment of the enormous revenue tax. Tax-free alcohol is ab- 
solutely necessary for the development of our industries. The 
price at which it is obtainable at present is still about five times 



208 Schoch: Introductory Chemistry 

as great as that at which it could be furnished. In order to 
stimulate the manufacture of denatured alcohol, the U. S. Bureau 
of Chemistry has built and operated an experimental plant, and 
has thus determined the cost of such a plant and its operation. 
The results thus secured, together with direction for denaturing 
alcohol and all the legal requirements to be complied with in its 
manufacture, hare been published in Bulletin Xo. 130 of the 
Bureau of Chemistry, U. S. Department of Agriculture, entitled: 
"The Manufacture of Denatured Alcohol,'"' by II. W. Wiley. This 
bulletin is distributed free by the government. 

The object of defw.ti/rinr/ alcohol is to render it unfit for drink- 
ing. The denaturant must be repugnant to the state and intoler- 
able to the stomach — yet it should not be deadly; and it must be 
so difficult to remove from the alcohol that it will not pay to do it. 
The main formula for denaturing is: 10 parts of wood alcohol and 
one-half part of benzine to 100 parts of 90 per cent ethyl alcohol. 

18. Ethyl Ether. 

Ethers are compounds in which two carbons — one in each of 
two hydrocarbon radicals — are connected through an O atom — 
or in other words, by the two bonds of an O atom, — e. g. 



methvl ether, H— C— O— C— H 

! i 

H H 

H 3 C— CH 2 

ethvl ether, O 

I 
H 3 C— CH 2 

Ethers are made directly from alcohols: the reaction appears as 
a dehydration merely,— e/g. 2CH,OH=(CH,) 2 O^H 2 0. 

19. Illustration of the Preparation of Ordinary (Ethyl) Ether or 
Sulphuric Ether. 

Put a few c.c. of 95 per cent alcohol into a test-tube, insert a ther- 
mometer and add gradually an equal volume of concentrated sulphuric 
acid. Stir the mixture after each addition. Then heat it gently to 145 
degrees C. and observe the odor of the vapor issuing from the test-tube. 
This illustrates how ether is manufactured commercially. It appears as 
though the reaction were merely a dehydration of the alcohol. 

Ether, just like alcohol, is of great importance industrially — 
mainly as a solvent for fats, resins, etc., and also as an anesthetic. 
It has a very low boiling point (34.9° C.) and is very inflammable. 



Chapter XIII 209 

20. Aldehydes. 

Aldehydes are the direct products of oxidation of alcohols. The 
oxygen of the oxidizer acts on the "alcohol" group as indicated in 
the following equations: 

H 3 — C— 0— H +0 — >H 2 C=0 +H 2 
methyl formal- 

alcohol dehyde 

H S C—C— 0—H+O— >H 3 C— C=0 4-H 2 

I 
H 

ethyl acetal- 

alcohol dehyde 

The different aldehydes are named with reference to the acids 
that they are changed to on further oxidation, which for the above 
aldehydes are formic acid and acetic acid, respectively. 

Aldehydes are prepared, even commercially, by the oxidation of alco- 
hols. For an illustration of this simple action, mix 1 c.c. of ethyl alcohol 
with an equal volume of dilute sulphuric acid, put into the mixture a 
pinch or two of powdered potassium bichromate (an oxidizing agent!) 
and warm the mixture: the acetaldehyde formed reveals itself by a pun- 
gent, slightly sour odor (decidedly different from that of alcohol) and 
the change of the color of the mixture, from red to green, shows that the 
chromate has been reduced. * 

Formaldehyde is now very important in every-day life because 
its vapor is a powerful poison for bacteria, but not for higher 
forms of life, and since it penetrates through cloth and into every 
crevasse, without any injurious effects to fabrics, etc., it is used 
to disinfect dwellings which have been infected by disease bacteria. 
It is obtained commercially by the oxidation of wood alcohol. 

Coil some thin copper wire around a pencil, thus forming a spiral 
about three inches in length; hold this with the tongs in the top of a 
Bunsen burner flame to oxidize its surface thoroughly, and while hot 
drop it into a test-tube containing 1 c.c. of wood alcohol. Note the 
sharp odor of the formaldehyde formed. 

In the commercial preparation, a mixture of wood alcohol and 
air are brought in contact with hot copper oxide : the copper oxide 
oxidizes the alcohol, and then the air oxidizes the reduced copper 
again. Since air alone oxidizes wood alcohol very slowly, the cop- 
per oxide acts as a "catalyzer" or hastener of the action. It is 
now considered that all "catalyzers" are effective through such 
"intermediate" reaction. 

21. The Use of Formaldehyde as a Disinfectant. 

Formaldehyde is found in commerce in the form of a 40 per cent 
aqueous solution, called formalin. Its wholesale price is about 10 
cents a pound, and its retail price should be from 20 to 50 cents, 



pmir — 

■ uk nm 7". • . -■ 



■ • - ■ n •' -- 

air rif Snmm&m inn i± nun 

)T vnZi.Hi. \ •- '\'JZ\ ... t. - ..in vniLrv iv ;i t . -, on. n»-\-;u mr 

- 
if hi ••; 

:ii-.'n. Tifi — "ii-- 

ill:l "": r " Ll: -111 .1. T.i.' '.if 1-..1 ill .1.- 1 > <r ..lit lie nil'::.-' 11 I. Tilir 

• :f . i»: i .if! i ' ir ..■- i •-... .: . 
inmiL n ■■! i numif- 

•;ii- :;.. y'.l >-:::" wmmttk •'" .;• ' 'Ti . l. ■-•■:;...:; — -i , r ir 

-■■ : 

.1 unnun 



i 

- l nun 






•'";!' • : *:: 



. 



' 



Z — = - — = 

h -'•" ■ if' 

- ■ "■" ■ 



Chapter XIII 211 

formic acid; and next to this comes CH 3 COOH, acetic acid. The 
"carboxyl" group may be present more than once in a molecule. 
The hydrogen of the CO OH group is the "acid" hydrogen. 

Acetic acid, which is one of the most important of these acids, 
is one of the products obtained in the destructive distillation of 
wood (see Art. 37). It is also obtained by the fermentation of 
dilute aqueous solutions of ethyl alcohol. 

23. Genetic Relationship of Hydrocarbons, Alcohols, Aldehydes, 

and Organic Acids. 

« From an inspection of the foregoing articles (12, 20, and 22), 
it will be seen that an organic acid can be prepared from a hydro- 
carbon by means of the following steps: 

1. C 2 H G -hCl 2 — ► -CH ; — CH 2 C1+ H C1 

(hydrocarbon) (alkyl chloride) 

2. CH 3 — CH 2 — Cl+AgOH— ■ > CH 3 CH 2 — OH+AgCl 

(alcohol) 

3. CH 3 — CH — OH+O;— >- CH 3 — CH+H,0 

I I 

(aldehyde) 

4. CH 3 — CH+O — > CH 3 — C— OH. 

II II 



(organic acid) 

This relationship is perfectly general, and should be kept well 
in mind. The student will be asked to outline the scheme by 
which such acids as proprionic and butyric could be prepared 
from the proper hydrocarbons. 

24. Esters. 

A mixture of ethyl alcohol and acetic acid react slowly accord- 
ing to the following equation: 

H 3 C— C— OH +HO— C— CH 3 -> H 3 C— C— 0— C— CH 3 +H 2 

H 3 I ! H 2 | | 



or C 2 H 5 OH+CH 3 COOH=CH 3 COO.C 2 H 5 +H 2 

The new compound is composed of the alcohol radical and the 
acid radical: it has the C in the alcohol group linked by an 
atom to the C in the acid group. Compounds which contain such 
structures or which are thus made by the joining of alcohol and 
acid radicals are called esters. 



25. Preparation o: tixe Twn^n fisfaar iif Jkestic Ajcil. 

i 

ma 

in* n... 
piiuri 

I 

. . BuggBHtioiif or the IBuMj gonui Typm o: lompounflL 

D :. 

— 

pOUli 

in 

Z-xercist 
! 

The Aromatic o: Z^yclu &£- arboi lompounoE 

• cnmpoiE 

m 

p*oir 

onroouu 3 

- 
inoB : inpmmik art ealit-: zm " 

pram : - :. 

axon. 

JlIIjMlliUJQf niDOTHLQi. 

; 
"nam 



Chapter XIII 213 

The most important carbon ring or cycle found in these "cyclic" 
compounds is seen in its simplest form in the compound known 
as benzene or benzol, C H C , the theoretical structure of which is 
written thus: 

H H H 

! I I 
c— c=c 

II I 

c— c=c 

i ! I 

H H H 

The figure shows that every C atom is connected with four bonds 
to the other atoms — which is in accordance with one of the fun- 
damental ideas upon which the structure of all carbon compounds 
is worked out. 

These IPs which are directly on the benzol ring are easily acted 
upon by reagents, and through their reactions other elements or 
radicals are put in place of one or more of the EPs — e. g\, C 6 H 5 C1, 
C 6 H 5 OH, C 6 H 3 CH 3 , etc. As may hence be expected there exist 
many compounds with a benzene ring in their molecules. This 
benzene ring has decided characteristic properties and it influences 
the properties of its compounds so largely that all compounds 
containing a benzene ring have many properties in common. 

Besides the one-ring nucleus of which benzol is composed, there 
is a two-ring nucleus, naphthalene, C 10 H 8 , and two "three-ring" 
nuclei, C 14 H 10 , called anthracene and phenanthrene, with prop- 
erties similar to benzol, and which together with their compounds 
are included under "aromatic" compounds. 

29. The Commercial Source of Aromatic Compounds and Their 
General Properties. 

The commercial source of aromatic compounds is the product 
obtained in the distillation of bituminous coal in the gas and coke 
industry. This product consists of an aqueous portion contain- 
ing ammonia and of an oily portion containing the light aromatic 
oils and the coal tar. The oil portion is subjected to a frac- 
tional distillation and yields first a series of "light oils," which 
are lighter than water. It is usually known as coal-tar naphtha. 
It contains benzene together with some of the simplest hydro- 
carbon compounds. "When pure, benzene distills at 80.5° C, and 
has a specific gravity of 0.899 at 0° C. 

As the application of the heat to the tar still is continued and 
the lower boiling constituents distill out, the temperature rises, 
and higher boiling constituents pass over. When the specific grav- 
ity of the distillate has reached 1, then the receivers are changed; 
the temperature of the still is then from 170 to 190 degrees C. 



214 :och: Lsteobuctoey Chehistey 

The next fraction (called "middle oil") is con. 

tillates up to about 33C a - C. and contains among- other 

sun. Lie acid (CjILOH), and naphthal ene. T 

. are called "'heavy oils": they 
are used wholly or in part for th>. r aol — i 

the : :ve treatment of timber. Sometimes the 

■which distills above _ - ted separately in 

lire the solid anthracene which separates from it on 
The distillation is either it a temperature between 

and 300 I s n order that the mass remaining in the still 

may be used as • we r it may be carr: 

re hard / 

Properties and uses of the tar distillates: The light oils yield 
mainly benzene and some closely related hydrocarbons. 

When the "middle oil" fraction cools, naphthalene sepa: 
from it in crystalline flakes, and may be separated from th- 
portion by filtration, 

Xaphthalene is a powerful germicide, and is used for 
ing purT ell as for the manufacture of some dy 

The oil filtered from the naphthalene is treated with ca 
soda solution to extract the carbolic acid, and the aqueous extract 
is then acidified (with H,8 the experiment below). Thus 

the carbolic acid is liberated airain. and sir -rns a layer of 

oil on top of the aqueous liquid, it is readily separated from the 
latter. It is used either in this crude form, or after more refin- 
ing. The germicidal properties are well known. 

The "heavy oils" are composed mainly of chemically neutral 

bodies — i. e., they are neither acidic nor basic. However, they 

are all germicidal, a fact which has made them valuable as wood 

rvers, for which the hydrocarbons of the paraffin series are 

unsuitable because they are not germicidal. 

All componei b 'he coal tar oils belong to the aromatic : 
cyclic - r a of compounds. Hence they all — even the hydro- 
carb' -•: : readily with reagents such as nitric acid, sulphuric 

acid, the ha! n which reactions the H'a directb 

the cyclic group are attacked and replaced by other elemer^ 
radicals. Th:~ jreat reactivity of the cyclic hydrocar 
sents a striking contrast to the non-activity which charactc 
the straight chain hydrocarbons, — that is the petroleum com- 
pote: 

Pitch is an excellent binder, and is used - : ring material 
ad on paper, or impregnated with sand and gravel, 
halt paint" is made by k I ring hard pitch in crude benzol 
or naphtha. The latter evaporates readily, and leaves a smooth 
coat of pitch. This paint is used to protect iron structures, pipes, 
sinks, etc. It does not last well on exposure to light and air (it 
"alligators"), but it does well on material that is frequently re- 



Chapter XIII 215 

painted, or which is placed in the ground, as water and gas pipes. 
Such tar or asphalt paint must not contain much free carbon, 
because the latter tends to stimulate rusting on iron. Eaw tar is 
sometimes used to paint iron, but the ammonia, naphthalene, and 
possibly other substances present tend to corrode iron, and hence 
the use of raw tar is inadvisable. 

30. Tar Oil for the Preservation of Timber. 

The preservative treatment of timber is effected either by in- 
jecting a large quantity of an antiseptic liquid into the wood 
under pressure or by dipping the wood so as to allow the surface 
to absorb such a liquid. The liquid required for the second pro- 
cedure must naturally be one which withstands exposure to heat 
and rain perfectly: hence it should be composed of insoluble oils 
boiling above 270 degrees G. In neither treatment is it intended 
to form a protective coating or to attempt to exclude moisture : 
moisture can enter or leave such timbers freely, but contact with 
these fungicidal oils renders it sterile, and thus inhibits the growth 
of wood-decaying fungi. 

A great many steam railroad ties are impregnated under pres- 
sure with a solution of zinc chloride. This salt is a fungicide, 
•and preserves ties fairly well in dry countries, though not for as 
long a time as creosote. 

Creosote is an indefinite term which designates vaguely an oil 
used for wood preservation : it may be anything from the volatile 
portion of the tar distillates, which would soon evaporate on ex- 
posure, to the valuable, permanent high boiling* oils. In buying 
and selling creosote, its quality should be defined by a specifica- 
tion, — or better still, the term creosote oil should be dropped and 
the term tar oils should be substituted because everybody would 
realize immediately that the term is indefinite. 

It was formerly assumed that the preservative power of the 
heavy tar oils — creosote — was due to the tar acids and to the 
naphthalene in it and that certain amounts of these were required 
to be present in oils used for wood preserving, but recent analysis 
of well preserved timbers that have been in service for various 
lengths of time have revealed that the tar acids and naphthalene 
disappear from preserved timbers fairly soon after treatment (tar 
acids, by dissolution in water; naphthalene, by evaporation), 
while the higher boiling oils (particularly those which distill 
above 270 degrees C.) remain in the timber and preserve it. In 
explanation of this action of the high boiling oils it should be 
stated these oils are practically insoluble in water, non-volatile, 
and yet strongly germicidal. Hence modern specifications call for 
as low a per cent of tar acids and naphthalene and as high a per 
cent of high boiling oils as possible. 



SCHOCH: IXTEODrCl-OBT Chzmistbt 

31. The Production of Wood Preserving O* 1 - 
Practically all :: 

from its 01 that the tar _ - ■ . and 

the lati istilled nnti- I maa hard pitch. Hence 

this indnsti — 

amounT . ' _ " i 

32. Tar Oils: The World's Great Germicides. 

Tar oil' osed as fungicides and germicides, not only 

in the oris _-■"■- 

thalti • - - — - - 

in the form of an aqueous 
: which com 

similar snbsi - 

of tar oil or of "era: 

sprinklec ka and draim ...-.._ 

or they may -first be diluted wii 

"will - . \~: : 

r. 
aerves .itinar 

- 

:.queous =. - ■ - 

sawc effective germicidal "sweeping** compound. 

The commercial si made from the 

--enniridal petroletim oils, although these are not. as suitable 
for this purpose. 

S3. Experiment; ~ 1 ■* Oils. 

up the same distilling apparatus that -was used lor the distaBataom 
of crude petroleum. N 

ment of timber 77 or crude carbolic add into the dirtalfiag flask, mad pro- 
ceed to distill - 

mometer indicates 195 d \ pot a clean receiving flask oa the end 

of the condensing tube and collect the ■est 30 ex. (approximate 
the final temperature and put another clean receiving flask on the com 
densing tube and collect abo* i of the next distillate. Again note 

the final temperature. The first SO cc Trill contain a grea t dea l of the 
carbolic acid in the sample, and will be used to show the e x t raction of 
this acid, -while the " -ample will serve as a fair representative of 

ordinary heavy oil m ih which some of its properties and uses 

may be shown. 

34. The Extraction of Carbolic Add- 
To the 30 cc distillate obtained above add 20 ex. of a 30 per cent 
sodium hydroxide solution, stir the mixture vigorously and heat it to the 
boiling point: then alk- H i mL By means of a huge dropping fimr- 
nel separate the aqueous from the oily layer. Add another 10 ex. ©f 
sodium hydroxide solution to this oil. stir and heat the — i »i « re and 
separate it again. Then throw away the oily residue. 

Pour the caustic soda extract into a 250 cc flask, allow it to cool, add 



Chapter XIII 217 

dilute sulphuric acid to it slowly and shake the mixture thoroughly after 
each adidtion, and continue the addition of the acid until the mixture 
reacts acid to litmus. Then add water until the flask is filled well into 
the neck. Note that an oily layer will collect in the neck of the flask. 
Observe its odor. By what chemical reactions was it separated from the 
oil and liberated again? 

35. Demonstration of Some Properties of Tar Oils. 

Take the 70 c.c. distillate obtained above, cool it to the temperature of 
the tap water by allowing the latter to run on the outside of the flask 
and determine the specific gravity of the oil with the specific gravity bal- 
ance. Note the temperature of the oil while the specific gravity is be- 
ing measured. In recording this resiilt, state the temperature between 
which this sample was obtained on distillation and also the temperature 
at which the specific gravity was taken. Compare these data with the 
corresponding data on petroleum oils: — the specific gravities of coal tar 
fractions obtained above 200 degrees C. are always greater than 1.0, while 
the specific gravities of all petroleum distillates are less 1.0. This fact 
is used by chemists to ascertain whether or not wood preserving oils are 
pure tar oils or have been adulterated with crude petroleum. 

To contrast the great reactivity of tar oil with the non-activity of 
petroleum oils, put some 20 c.c. of this 70 c.c. sample into a separate 
small flask and put about 20 c.c. of regular petroleum oil into another 
flask. 

Add four to five times as much concentrated sulphuric acid to each oil, 
stir the mixtures vigorously and heat them gradually to about 60 degrees, 
then set them aside for about one-half hour, shaking them at intervals. 
Next take two large flasks, fill them one-half full of tap water and then 
pour one of these mixtures gradually into one flask, and the other into 
the second flask. Finally fill both flasks with water well into the neck 
and allow them to stand undisturbed for several hours. In the flask con- 
taining the petroleum oil almost the whole of the original sample will 
reappear in the neck, while in the other flask practically none of the tar 
oil will appear, which shows that the petroleum oils are very slightly 
attacked by the concentrated sulphuric acid, while the tar oils are com- 
pletely attacked and converted into water-soluble compounds. 

36. The Preparation of Tar Oil Disinfectants and Germicides. 

Cut about 25 grams of rosin soap into fine shavings, add an equal 
weight of distilled water, and warm and stir the mixture until the soap 
has been dissolved. Then add an equal volume of crude tar oil, heat and 
stir the mixture: a solution of the appearance of black coffee will be 
obtained. 

This solution was referred to in the descriptive matter above. It has 
great germicidal power and is found in the trade under such names as 
chloro-naphtholeum, creoline, etc. 

Mix some of this black solution with about fifty times its volume of 
water: — the mixture will become milk white, will clear up on standing 
and it will then be found that the tar oil has settled out to the bottom. 
The surface forces of this dilute soap solution are not able to "dissolve" 
the oil — hence it separates, at first in very small globules, which give the 
mixture the milk white appearance. 

37. Chemical Products Made by Distillation from Wood and Resins. 

To complete the list of chemical manufactures based on the dis- 
tillation of raw materials, mention should be made of the manu- 
facture of turpentine, rosin, rosin oil, charcoal, wood alcohol, 



i!5 :och: Lstbodtctort Ckeujstry 

acetic acid, and acetone, — all of which are commercially extremely 
iL'.y'.-rr.iJi: i... -.. : ~y.._ .. -:- :-.:::•:_ :r:n —-...;. 1 - :::- :.-.--.- 
:_ ,-■::.--.'.. 

The resins obtained by "bleeding" or "boxing" resinous pine 
and fir trees are mixed with water and the mixture is distilled: 
the distillate contains a mixture of oils which is commercially 
known as "gum" turpentine, and the simplest representatr 
which has the formula C 1# H ?€ . These oils are evidently unsatu- 
rated hydrocarbons. The residue left in the retort is the rosin or 
colophony of commerce. 

When rosin is subjected to further dry distillation, it yields 
a distillate called rosin oiL which is used to make axle grease, and 
it is also used as a cheap (worthless) substitute for linseed oil 
in paints. 

The destructive distillation of non-resinous wood yields the fol- 

(a) An aqueous distillate called pyroligenous acid, which con- 
tains, among other ingredients, acetic acid and wood alcohoL 

(b) Wood tar. for which therv little special use, and 
which is used for fuel mosl 

Charcoal, which remains as a residue in the retort 
:be wood is resinous, it is first mixed with water and then 
subjected to distillation. The large amount of steam firs: 
tilled carries with it the turpentine from the resin in the wood; 
and tjiis portion of the distillate is collected separately. The sub- 
sequent "dry" distillation of this wood yields about the same 
products as the distillation of the nonresinous wood just described 
above. The turpentine obtained in this distillation is called wood 
turpentine : it has a higher boiling point than the gum turpen- 
tine, but is chemically quite similar to the latter. 

Distillate (a), the pyroligenous acid, has the acid in it neutral- 
ized with lime, then die wood alcohol is distilled out of it, and 
finally the water is evaporated to obtain dry acetate of lime. The 
latter is used largely to make acetic acid (by treatment with sul- 
phuric acid and distillation i : calcium acetate is also distilled dry, 
under which condition it yields a distillate of acetone (CH 
a commercially important liquid, which is formed according to 
':.- ::■"-' .:._• ::::'• 



II 

CH— C— O CH, 

— CaCO.— 
CH,.— C— CH, 



Chapter XIII 219 

Questions on Chapter XIII. 

1. Figure out as shown in Art. 2 how many different com- 
pounds with the formula C 6 H 14 are theoretically possible. 

2. Give two different names for the compound of the formula 
CH 3 C1, and give the complete equation for its formation by the 
interaction of chlorine and methane. If CC1 4 is made by the 
action of chlorine on methane, then how many grams of HC1 are 
produced while one gram of CC1 4 is produced? 

3. One gram of ethylene, C 2 H 4 , is converted to the corre- 
sponding saturated compound by treatment with chlorine gas. 
Calculate how many grams of the resulting product are obtained. 

4. State exactly what is meant by a crude oil having a par- 
affin base, or having an asphalt base. How is the binding power 
of asphalt or crude oil residue used for road building "meas- 
ured?" By what measurements are lubricating oils measured? 
How is prafnn manufactured: state exactly. Why is sulphur ob- 
jectionable in gasoline or kerosene : explain the chemical action 
that takes place in the removal of sulphur from such oils? If 
you were looking for a material with which to paint table tops, 
etc., in order to protect them against the action of chemicals, 
would you take a varnish, the chief constituent of which is a 
resin similar to rosin in chemical property, or would you take an 
oil like linseed oil, or would you choose some other fatty or waxy 
material: state which and why? 

5. Draw all the structural possibilities for an alcohol of the 
composition C 3 H 7 OH. 

6. Give the structural formula of propyl ether and state with 
which substances and what operations it would be produced. 

7. Give the structural formula, of the propyl ester of pro- 
pionic acid and state from what substance and what operation 
it would be produced. 

8. How is the disinfectant known as cresol made? What is 
creosote: define the characteristic of a first-class quality of creo- 
sote. Why do tar oils preserve wood? What is the formula of 
carbolid acid? of sodium carbonate? Write the reaction which 
takes place in the extraction of carbolic acid from tar distillates 
by means of caustic soda solutions. 

9. What is rosin oil? For what is it frequently substituted? 



220 S hock: Intteoductoby Chemistey 



CHAPTER XIV. 

APPLIED ORGANIC CHEMISTRY: ANIMAL AND VEGETABLE 
EATS AND OILS, CARBOHYDRATES. AND NITROG- 
ENOUS POOD CONSTITUENTS. 

1. Properties and Uses of Some Important Oils of Animal and 
Vegetable Origin. 

The vegtable and the animal fats and oils have the same gen- 
eral composition: they are mixtures of glycerin esters of several 
"straight-chain" carbon acids. The fatty acids which make up 
the greater part of these fats have from 16 to IS C*s to the mole- 
cule, and only one carboxyl (COOH) group. Glycerin is a tri- 
bydroxyl alcohol. ( H 5 (OH)„ henoe it reacts with three mole- 
cules of the '"fatty" acids according to the following equation : 

3 BCOOH+C H-<<->II | =C,H,(El 00 - BLO 

Here R represents the rest of the acid molecule except COOH. 
and is a hydrocarbon radical. The formula C.H. (RCOO 
presses the composition of all fats and oils of animal and 
table origin. 

Glycerides of the following acids are found as components of 

be md oils. 

Saturated acids: 

Butyric acid. C IT. COOQ 
Laurie acid. CjH COOH 
Palmitic acid. C«H 81 COOH 
Stearic acid. c.-H . COOH 

Unsaturated acids: In all of the following unsaturated acids 
the hydrocarbon radical contains IT C. hence if they were satu- 
rated t*he hydrocarbon radical in each one would contain 35 H. 
as in stearic acid above: the number of H which they have less 
than 35 indicates the amount of unsaturaticn in the acid mole- 
cule — 

Oleic acid, C 17 H S3 COOH. amount of unsaturation. 2H. or one 
double bond. 

Linoleic acid. C 17 H S1 COOH. amount of unsaturation. 4H. or 
two double bonds. 

Linoleinic acid. C-H : ... COOH. amount of unsaturation. 6H. or 
three double bonds. 

The glycerides of palmitic acid (palniitm) and of stearic acids 
(stearin) are white crystalline solids, melting at 61 and 72 de- 
grees C. respectively: that of oleic acid (olein) melts at 14 de- 
grees C. and hence is liquid at ordinary temperatures, and the 
glycerides of linoleic and of linoleinic acids have probably still 



Chapter XIV 221 

Jower melting points. The solid fats are composed in large part 
of stearin or of palmitin or of both, while the liquid oils are com- 
posed largely of olein, linolein, etc. 

Fresh fats and oils are nearly odorless and neutral in reaction, 
but when exposed to the air small portions are frequently "hydro- 
lyzed" by the moisture of the atmosphere, and thus a small 
amount of the free fatty acids and of glycerin are formed. This 
action is usually induced by the fermentation or putrefaction of 
substances of a gelatinous or albuminous nature which are always 
present in raw fats and oils, and is accompanied by numerous 
secondary reactions which produce small amounts of bodies of 
disagreeable odor and taste. The oil is then said to be rancid. 
In "refining" vegetable oils: e. g., cotton seed oil, the albumin- 
ous bodies are removed and hence the refined oil does not become 
rancid as readily as unrefined oil. 

The fats and oils are specifically lighter than water. They can- 
not be boiled or distilled, even under reduced pressure; heated 
much above their melting point, they decompose into various sub- 
stances. 

The glycerides of the unsaturated acids — particularly those of 
linoleic and linoleinic acids — take up rapidly, or react energetically 
with, oxygen^ iodine, sulphuric acid, etc. The substances combine 
with the oil molecules at the double or triple bond, just as HC1 
combines with ethylene, CH 2 CH 2 to form CH 3 CH 2 C1, and bro- 
mine combines with acetylene to form CHBr 2 CHBr 2 . When oxy- 
gen combines with such glycerides at the point of "unsaturation," 
thick, gummy or resinous masses are formed, which in thin layers 
become hard, dry, transparent or translucent films, and the change 
is hence commonly called "drying" — e. g., as in the drying of oil 
paints, etc. 

2. The Manufacture and Properties of Cotton Seed Oil. 

Cotton seed oil is a mixture of glycerides of fatty acids in which 
the liquid glycerides (e. g., olein) predominate. It contains ap- 
proximately 22 to 31 per cent of saturated compounds (mostly 
palmitin with a little stearin), 59 to 52 per cent of olein (one 
double bond in each acid radical), and 19 to 16 per cent of linolein 
(two double bonds in each acid radical). The glyceride of lino- 
leinic acid (with three double bonds in the acid radical) is prac- 
tically absent. On account of the absence of the last named 
glyceride and the predominance of the slightly unsaturated olein, 
cotton seed oil does not dry to a film as linseed oil does (see be- 
low), yet it becomes viscous when it is oxidized (by the air). 

The manufacture of cotton seed oil: Fresh cotton seed is 
cleaned by passing it first through a screen with a mesh slightly 
larger than the seed, and then over a screen with a mesh slightly 
smaller than the seed: thus, objects both larger and smaller than 



222 Schoch: Introductory Chemistry 

the seed are removed. It is then "re-ginned" to remove the lint. 
and then de-hulled. Finally the meats are crushed between rollers. 

The per cent of the different substances thus obtained from the 
seed are as follows: Hulls, 48.9 per cent; linters, 1.1 per cent: 
crushed meats, 50 per cent. The latter yields about one-fourth 
oil and three-fourths meal. 

To prepare the cotton seed meats for the press, the meats are 
first cooked. The purpose of this is to modify the consistency of 
the meats through heat so that the oil may be expressed as com- 
pletely as possible. The heat also expels the excess of moisture and 
coagulates the albumen. The cooked meats are then molded into 
cakes to fit the press, and finally tli" «»-l is pressed out by means 
of hydraulic pressure. The cakefl taken out of the press are then 
ground up into the cotton seed meal, which is a valuable feedstuff. 

The crude oil is reddish brown in color, and contains impurities. 
These ferment or putrefy readily and induce the liberation of free 
fatty acids and other products which make the oil rancid. The 
amount of free fatty acid in oil is hence an indication of its 
and in commerce its determination is frequently required. Since 
with the removal of the impurities the tendency for the oil to 
become rancid becomes much less, this refining is undertaken as 
early as possible. In this operation a certain — variable 1 — amount 
of oil i- lost together with the impurities ; h.mee the value of the 
crude oil depends on the "refining loss." The determination of 
the amount of this loss in any particular lot of oil is shown below. 

After refining, the oil must be thoroughly dried, first by warm- 
ing and then by adding plaster of Paris to the oil. This takes up 
the water as "water of crvstallization," forming CaS0 4 , 2ELO. 
The result is "summer yellow oil/* 

The yellow oil is bleached by means of fuller's earth: the finely 
powdered earth is stirred into the oil. and the latter warmed 
gently. Then the oil is filtered. This gives "summer white oil." 

The summer white oil is then chilled and the solid palmitin and 
stearin (known as cotton seed stearin) separated from the oil by 
filtration. The clear light-colored oil (known as "winter oil") is 
extensively used as a salad oil. Except for a slight difference in 
flavor, it can be used, in cooking, for everything that olive oil can 
be used for, and it is even more completely digested than olive oil. 
(The digestion coefficient of cotton oil is 93.5 per cent, while that 
of olive oil is only 89 per cent.) 

3. Products of Cottonseed Oil: Lard Compound, Hardened Cotton- 
seed Oil, Oleomargarine, Etc. 

Just as a solid and an oily portion may be obtained from the 
cotton seed oil, so thev may be obtained from beef fat (tallow). 
These products of tallow are known as oleo-stearin and oleo-oil. 
respectively. "Lard compounds" are mixtures of "summer white" 



Chapter XIV 223 

cotton seed oil (which contains all its stearin, etc.) and oleo-stearin. 
Sometimes hard stearin is used in place of oleo-stearin. Lard- 
stearin is manufactured from lard just as oleo-stearin is obtained 
from tallow. Lard compound is made chiefly by the packing 
houses, as it is a convenient and profitable way to dispose of their 
large amounts of beef tallow obtained in the slaughtering of cattle. 

Hardened cotton seed oil is now being manufactured in large 
quantities in the United States. Cotton seed oil consists prin- 
cipally of olein (the glycerine ester of oleic acid) ; oleic acid is an 
unsaturated acid, as an inspection of the formula, C 17 H 33 COOH, 
will reveal. The amount of unsaturation is 2 (i. e., the molecule 
of oleic acid is capable of taking up 2 additional hydrogens). If 
these two hydrogens are actually taken up by the molecule of oleic 
acid, it is changed from oleic acid to stearic acid, C 17 H 35 COOH > 
which is a saturated acid. The glycerine ester of stearic acid is 
a solid at room temperatures and somewhat above. Thus, the 
process of hardening cotton seed oil is one of hydro genation; the 
process consists simply in the adding on of six hydrogens to the 
molecule of olein, two hydrogens for each molecule of oleic acid 
in the molecule of olein. The patents covering the process are 
patents governing the method by which the hydrogen (in the form 
of gas) is caused to add on. "Crisco" and "Crusto" are examples 
of the many trade names under which this hardened cotton seeo* 
oil is put on the market for consumption. 

Peanut oil is similarly hardened, and also produces a nice, firm 
white "lard." Eepresentative of this type is the trade article 
"Pindapan." 

Cotton seed oil is also used in making oleomargarine. One- 
formula for making this butter substitute runs as follows: 

Oleo oil 495 pounds 

Lard 265 pounds 

Cotton seed oi] (summer yellow) 315 pounds 

Milk ^ 255 pounds 

Salt 120 pounds 

Color 1 J pounds. 

These substances are merely mixed mechanically. 
Cotton seed oil, particularly those grades which have undesir-- 
able flavors or colors, are used to make soap. 

4. Methods for the Determination of the Amount of Oil in Cotton 
Seed and Cotton Seed Meal. 

At present cotton seed is bought and sold blindly — without any 
consideration of the quantity and quality of the oil contained in it. 
The following directions show that determinations suitable for the 
trade may be made without difficulty even by people who have had 
but little chemical training. By means of such analyses the buy- 



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Chapter XIV 225 

6. Demonstration of the Refining of Cotton Seed Oil. 

The refining of cotton oil has for its object the removal of any 
free fatty acids that may have been formed (by the action of 
moisture and ferments) and of the albuminous matter introduced 
from the seed. It is accomplished by converting the free acids 
and a little of the oil into soap. As the little globules of soap, 
which are at first spread uniformly throughout the oil, — as they 
collect and form larger particles and finally settle to the bottom, 
the mucilaginous impurities are drawn along and collected with 
them. 

Secure 5 c.c. of a 10 per cent solution of sodium hydroxide, and also 
75 c.c. of raw cotton oil. Put the oil into a small flask or bottle and 
while shaking the oil, gently but constantly, add the sodium hydroxide 
solution in portions of a few drops at a time. Then warm the mixture 
by placing the flask in hot water but do not allow it to become so hot 
that it cannot be held against the skin; continue to stir until the mix- 
ture shows a tendency to clarify by the settling out of the soap stock. 
Allow the latter to settle out thoroughly, decant the clear oil and pre- 
serve it for the next operation. 

7. Demonstration of the Bleaching of Cotton Seed Oil. 

To the refined oil prepared above add approximately three to ten grams 
of finely powdered fuller's earth. Stir and warm the mixture in hot 
water and filter it through a dry filter paper. The oil should have be- 
come much paler, — if not, the operation should be repeated and possibly 
a larger quantity of fuller's earth should be used. The action of the 
fuller's earth is due purely to surface forces. 

8. Separation of the Cotton Oil Stearin. 

Put into a test-tube some of the bleached oil just obtained and cool it 
in ice water until its temperature is practically at degree C. : those 
components of the oil which have high melting points will solidify and 
may be removed by nitration. This solid portion is mostly palmitin. 

9. The Manufacture of Soap. 

The soap stock — fatty material — required for soap making varies 
according to the kind of soap desired. For white, hard soaps, the 
best grades of tallow, palm oil, or cocoanut oils are used. Cotton 
seed oil mixed with tallow or lard also makes an excellent soap 
stock for white hard soap. A soap stock for hard soaps must con- 
tain a large proportion of the non-drying oils (stearin, palmitin, 
etc.) ; the sodium salts of these acids are hard, while the sodium 
salts of drying oils (olein, etc.), are soft like butter, and hence the 
latter must not be present in too large a proportion in the stock 
for hard soap. 

A good soap should be free of disagreeable odors, free from un- 
combined caustic soda and also free from uncombined fat; it 
should be uniform in texture, and should not contain a noticeable 



226 Schoch: Introductory Chemistry 

amount of foreign substances (filler!). A pure white color also 
is an indication of good quality. 

Perfumes, colors and other materials added to soap as in medi- 
cated soaps seldom add anything to the value of the soap, and 
frequently they are added merely to mislead the public into buy- 
ing an inferior article or to pay an unnecessarily high price. , Pure, 
good soap is a staple article that can be had at a very low price 
if bought of the proper source. 

Hard soaps are made invariably by means of soda, and by "salt- 
ing" the soap out of the reaction mixture — thus removing the 
glycerin and other — accidental — by-products. The method of 
preparation is demonstrated below. 

In the manufacture of soft soaps, the soap stock is selected so 
as to contain mostly glycerides of unsaturated acids; e. g., linseed 
oil, cotton seed oil, etc. Furthermore, these soft soaps are made 
either by means of potash, or, if made with soda, they are not 
"salted" out, so that they contain the glycerin, etc. 

Soap for differenl purposes and saponaceous compounds, such 
as pcarline, sapolio, etc., are composed of the following substances: 

Soft soaps. — Potash soap, together with the whole reaction mix- 
ture; i. e., glycerine and water. 

Filled or padded soap. — Soda soap with the whole reaction mix- 
ture and frequentlv also impalpable earth powders or water 
glass (sodium silicate). 

Pure, white, hard soaps of best quality. — Xothing but soap mate- 
rial carefully prepared so as not to contain an excess of alkali 
or of free fat (by repeated boiling, with careful adjustment 
of "stock" to lye.) It is heavier than water, but by stirring 
air into it, it can be made to float on water. 

Laundry soap. — Contains, besides soap, an excess of alkali, which 
is desirable for laundry purposes, but to be avoided for toilet 
purposes. The excess of lye is incorporated in the soap by 
deliberate manipulation. 

Yellow soaps. — All yellow soaps are made by using rosin for a part 
of the soap stock. 

Toilet soaps. — (a) Pure, white soap of best quality (see above) 
is best for. a toilet soap. A not undesirable addition is that 
of some free oil or vaseline to the soap : this makes the soap 
"lather" well. 

(b) Medicated or scented soaps are merely ordinary soaps 
with the drugs or perfumes mechanically incorporated. 

(c) Transparent soaps: These are prepared without heat- 
ing ^he reaction mixture. This is possible by the use of a 
readily reacting soap stock — such as castor oil — or by the use 
of alcohol as a solvent for the fat. The soap contains all the 



Chapter XIV 227 

reacting mixture, and usually an extra amount of glycerine is 
added. The transparency is due to the presence of the 
glycerin. 

(d) Liquid soaps: These are merely dilute aqueous solu^ 
tions- of soap. 

Soap powders, sapolio, etc. — These contain gritty earthy sub- 
stances bound together with a small amount of soap. They 
usually contain an excess of free alkali. 

10. The Preparation of Hard Soap. 

Secure about 35 grams of tallow and 15 grams of "summer oil" and 7 
grams of caustic soda. Dissolve the latter in 35 c.c. of water: then take 
one-fourth of this and dilute it to 25 c.c. and put it into a medium-sized 
beaker. Melt the fat by warming it gently in a small dish, and pour it 
into the beaker containing the 25 c.c. of dilute solution. Heat and stir 
this mixture until it is thoroughly mixed, then add gradually the rest of 
the caustic soda (the concentrated solution), and continue to heat it, 
with gentle stirring, until a sample clinging to the stirring rod feels dry 
and firm between the fingers. About 40 c.c. of strong salt solution (25 
per cent) is then to be stirred into the mixture to "salt out" the soap. 
The contents now should divide themselves into two layers, the upper 
consisting of soap paste (with water) and the lower consisting of the 
aqueous solutions of the salts and glycerin. 

11. The Determination of the Main Constituents of Soap. 

The following exercise is intended to enable students to find 
out for themselves the chief components of ordinary soap and soap 
powders, etc.; it is also intended as an illustration of how such 
work is done. However, students should not mislead themselves 
into believing that these directions suffice to determine all com- 
ponents, nor to believe that these exercises can make expert ana- 
lysts out of elementary students : — the exercises merely show some- 
thing of the methods which a chemist employs in making analyses 
of such substances as soap. 

In this exercise the following components are to be determined : 

(a) Insoluble matter, — sand, clay, etc. 

(b) Total soap stock (sodium salts of fatty acids). 

(c) Free alkali. 

The amount of water, of undecomposed fat, and of glycerin 
which may be present are ignored in these determinations. In 
most commercial soaps, free fat and glycerin are practically absent. 

(a) Insoluble Matter: The sample to be used should be reduced to 
fine shavings or to a fine powder. Weigh out in a 250 c.c. flask 10 
grams of any white laundry soap or 10 grams of "Lava" soap. Add 50 
c.c. or more of hot distilled water and digest the mass over a mild source 
of heat until the soap stock seems to have dissolved. If an insoluble resi- 
due remains, decant the liquid into a beaker, treat the residue with an- 
other, smaller portion of hot water, and if necessary treat it with a third 
portion of water. Of course the different portions of water are all col- 



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Chapter XIV 229 

are ripe, and hence the latter, before they are pressed, must be 
allowed to ripen after being gathered. The seed which has ripened 
in the fields yields the best oil. 

The seeds may be pressed cold or hot, or first cold and then 
again hot. Cold -pressed oil is pale and tasteless, and is used for 
cooking in Russia. The hot-pressed oil is amber colored or dark 
yellow. 

Linseed oil is the most important of the "drying" oils. It con- 
tains a few per cent only of the glycerides of saturated acids 
(palmitin, etc.), and the remainder is made up approximately 
as follows: 5 per cent of olein (one double bond in the acid 
radical), 15 per cent of linolein (two double bonds in the acid 
radical) and about 80 per cent of glycerides of acids, the unsat- 
uration of which is equal to three double bonds in each acid rad- 
ical. It is seen that linseed oil is composed almost entirely of 
glycerides of highly unsaturated acids which take up oxygen, 
iodine, etc., readily at the double or triple bonds in the mole- 
cules. "With the progress of the absorption of oxygen, linseed oil 
becomes thick, and in thin films, changes finally to a dry, hard 
substance. This change naturally takes place more rapidly at 
higher temperatures, and hence by "boiling" the oil, and blowing 
or "stirring in" air during the boiling, it is largely "oxidized," so 
that such "hoiled oil" (frequently called "hard oil") when it is 
spread out on a surface in a thin film requires only a short time 
to "dry." The boiling may be carried on to various extents : thus 
ordinary "boiled oil" for painting is obtained by "boiling" the 
oil until it has lost from 8 to 10 per cent of its weight, during 
which operation its temperature will rise gradually from 130 to 
200 degrees C. approximately: or it may be "boiled" until the 
temperature rises to 260 degrees and even higher. The extent of 
boiling is determined by the use for which the product is to be 
used — e. g., as a varnish, or for printers' ink (with lamp black or 
other pigments), or to make oil cloth or linoleum. 

Precaution : Linseed oil spread in thin films reacts so rapidly 
with oxygen and this reaction gives out so much heat that rags 
and paper which have been used to clean up paint spots, etc., 
frequently are ignited from this heat, and, if thrown around pro- 
miscuously, may start disastrous fires. 

This reaction of linseed oil with oxygen is catalyzed enormously 
by small amounts of lead or manganese compounds dissolved in 
the oil. Dilute solutions of lead or manganese rosinate or borate 
in linseed oil are called japans or driers, and when small amounts 
of one of these is added to raw linseed oil, then films of the latter 
will "dry" in about twenty-four hours or so, when films of raw 
linseed oil without a "drier" will require about three days. "Hence 
a "'drier" is added to all paints. This catalyzing influence of lead 
or manganese compounds is made use of in preparing boiled oil: 



230 Schoch : Ixtkoductory Chemistry 

when a small amount of lead oxide or resinate is added to the oil 
it need not be heated to so high a temperature to oxidize it rap- 
idly, and hence a lighter colored product is obtained. 

Since linseed oil commands a higher price than many other oils, 
and since no other oil is as well suited as a "pigment binder" in 
paints, it becomes necessary to test the oil used in paints. For 
this purpose the determinations of the Maumene number and of 
the iodine absorption number are best suited because the reactions 
in these tests involve only the double or triple bonds in the unsat- 
urated acids, and hence "measure" the extent to which the sample 
has the property of "drying" — which is the valuable property of 
linseed oil. 

In the examination of a supposed linseed oil, the specific gravity 
should also be taken. It is true that different samples of true 
linseed oil may show considerable variation in the specific gravity 
and that the other oils, such as cotton seed oil, etc., have so nearly 
the same specific gravity that an admixture of the latter to linseed 
oil would not be detected, yet with the addition of some other oil, 
such as rosin oil, which lias a considerably different specific grav- 
ity, the specific gravity determination reveals the adulteration bo 
readily that it always is advisable to make this test. 

13. The Maumene Test. 

The Maumene number of an oil is the number of centigrade 
degrees rise in temperature caused by mixing 10 ex. of concen- 
trated sulphuric arid with 50 grams of the oil. This determina- 
tion would be quite accurate and fixed if the concentrated sul- 
phuric acid would always be of the same strength of concentra- 
tion. Unfortunately, "concentrated" sulphuric acid does not al- 
ways contain the same amount of water: hence, in order to elimi- 
nate the errors due to a variation in this per cent of water, a fur- 
ther determination is made, using the same amount of acid but 
substituting 50 grams of water for the oil. The rise in temper- 
ature of the oil mixture divided by the rise in temperature of the 
water mixture gives a number which is not subject to the same 
variation as the true Maumene number. This number multi- 
plied by 100 is known as the Maumene Specific Temperature Re- 
action and is by far the more reliable determination of the two. 
The table in Art. 16 presents both the Maumene number and the 
Maumene specific temperature reaction for comparison. 

To make a test, weigh out in a beaker of approximately 150 c.c. ca- 
pacity, 50 grams of an oil such as cotton seed oil, or 25 grams of an oil 
such 'as linseed oil. Add to the latter 25 grams of kerosene, so that all 
samples have the same volume. The smaller amount of an oil such as 
linseed oil is necessary on account of the greater extent of reaction, of 
the highly unsaturated oils. Avith sulphuric acid. Surround the beaker 
loosely with cotton batting and place it inside of a larger beaker, into 
which it should fit fairly well. Observe the temperature of the oil. Then 



Chapter XIV 231 

add gradually from a burette 10 c.c. of concentrated sulphuric acid, and 
at the same time stir the mixture thoroughly with the thermometer. Con- 
tinue to stir as long as the temperature rises, and note the highest point 
at which the thermometer remains constant for any appreciable length of 
time. The difference between this and the initial temperature is the "rise 
of temperature." Then clean and dry the beaker, and repeat the experi- 
ment with 50 grams (50 c.c.) of water in place of the oil. If 50 grams 
was the amount of the sample taken, then the Maumene Specific Tem- 
perature Reaction is obtained by dividing the "rise" obtained with the 
oil by the "rise" obtained with water and multiply the result by 100. 
If only 25 grams was the amount of the sample taken and 25 grams of 
kerosene were added, then a separate extra experiment must be made as 
follows: take 50 grams of kerosene and determine the rise obtained when 
10 c.c. of the concentrated acid are added to it. The Maumene Specific 
Temperature Reaction of the 25-gram sample is then obtained by subtract- 
ing one-half of the rise obtained with kerosene alone from the rise ob* 
tained with the oil sample, multiplying the remainder by 2, dividing this 
product by the rise obtained with water, and finally multiplying by 100. 

Iii explanation of this test) it should be pointed out that this 
reaction of H 2 S0 4 with the acid molecules at the points of unsat- 
uration is evidently one that evolves heat, and the amount of this 
""heat effect" is, as always, proportional to the amount of reaction 
product. Since with different pieces of apparatus the same amount 
of heat (in calories) will raise the temperature of the whole 
through a different "rise" of temperature, it becomes necessary to 
determine the amount of rise with a certain amount of heat. For 
this purpose the determination with water is made, and by divid- 
ing the rise with water into the rise with oil, the results of the 
determinations are made independent of the apparatus (also in- 
dependent of the concentration of the sulphuric acid used). 

14. Demonstration of the Drying- of Linseed Oil (Painter's Drying 

Test). 

Secure three small pieces of glass and spread on them with a glass rod 
as thin a film of oil as possible: use (1) raw linseed oil, (2) boiled lin- 
seed oil, and (3) cotton seed oil. Place the slabs in a nearly vertical 
position in your desk. Note the time in days in which the film attains 
such hardness that the finger does not stick to it when it is touched. 

15. Illustrations of the Methods Used in Examining and Distin- 

guishing Between Linseed Oil and Similar Oils. 

Linseed oil in paints is frequently adulterated with, or replaced 
by, corn oil, cotton seed oil, fish oil, soya bean oil, and rosin oil. 
The following are some of the most important means used by 
chemists to distinguish between these oils or to ascertain if they 
are essentially pure. These methods are mainly quantitative, since 
qualitative tests are of little value due to the fact that they do 
not reveal the extent of the adulteration. Slight amounts of adul- 
teration are often negligible, and hence only the quantitative test 
is of value. The principal tests are (a) Iodine absorption num- 
ber, (b) Maumene specific temperature reaction, (c) specific grav- 
ity, and (d) some qualitative tests such as color and odor tests. 



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tingmshing k from finseeed oQ, since the constants for fish oil 
closely approximate those of fiaaecd oiL Fish oil should be ab- 

7 - ■■ :..-::: ■"-.!.-■.- -- - --: - :":-:;- :r :-r :•: ill z ;-- :~ 

Best a little of tie oil nearly to ItT C. aad rub in on tie bade of 



; rtion of color reveals the presence of rosin o€L 

■ 
rat 

riisrfe adulteration of 

- - - 

Warm 1 ie oil and add aa equal 

- - . ---:- - 



Chapter XIV 233 

add one drop of concentrated sulphuric acid: pure linseed oil gives a sea 
green color, but when adulterated with rosin oil a violet color shows it- 
self temporarily. 

16. The Constants of Some Oils. 

The following table of constants serve to distinguish the various 
commercial oils. In cases where these constants do not differen- 
tiate, it becomes necessary to employ other tests, partially men- 
tioned in Art. 15: 

Name of Oil Gravity at Maumene Spec. Temp. Iodine 

15° C. Number Reaction Number 

Linseed oil (raw) 0.931-0.937 103-130° 313-350 170-200 

Linseed oil (boiled) ...0.936-0.938 98-100° 242-248 150-175 

China wood oil 0.938-0.946 120-128° 327-330 163-178 

Fish oil . . : 0.927-0.933 123-128° 290-330 148-180 

Soya bean oil 0.923-0.924 88- 92° 229-240 127-136 

Cotton seed oil 0.921-0.930 70- 90° 163-170 101-117 

Corn oil 0.921-0.927 70- 90° 163-170 111-125 

Rosin oil 0.987-1.000 30- 32° SO- 83 40- 65 

An inspection of the above table will reveal that linseed oil, 
fish oil, and China wood (Tung) oil can be classed together 
as drying oils, Soya bean and cotton seed oil as semi-drying, and 
corn and rosin as non-drying oils. 

17. Carbohydrates: Their Mutual Relations and Properties. 

The carbohydrates are straight-chain compounds of carbon, hy- 
drogen, and oxygen only, in which the hydrogen and oxygen are 
present in just the ratio to form water; hence the name. 

Their proximate constituent, into which they may be all re- 
solved more or less directly or readily— -is a six-carbon group 
(C 6 H 10 O 5 ). With reference to this constituent, carbohydrates 
are thus classified: 

(a) Monosaccharides or glucose, C 6 H 12 6 ; i. e., C 6 H 10 5 +H 2 0. 
Of these, grape sugar and fruit sugar are familiar examples. Five 
of the carbons have alcohol groupings, and the sixth — an end 
group — has an aldehyde grouping. Glucoses are usually found in 
commerce in the form of syrups, because they do not crystallize 
readily. Their sweetness is only three-fifths of that of cane sugar. 

(b) Disaccharides or saccharoses, C 12 H 22 1;I ; i. e., 2C o H 10 O :t 
+H 2 0. Of these, cane sugar and milk sugar are familiar ex- 
amples. 

(c) Polysaccharides (C 6 H 10 O-)n. This group includes (1) 
starches and (2) cellulose, or woody fibers. 

18. The Change of Poly- and Disaccharides Into Monosaccharides. 

In hot acidified solutions, the members of groups (c) and (b) 
all change to glucose or monosaccharides. This change is under- 



234 S HOCH : IXTEOrrCTOEY -tey 

gone quite readily by cane sugar, slowly by starch, and r< 
by cellulose. In neut: I -. - - .ydro- 

much more &owb I at the high temperatures attained 

under pressure in closed vessels, and which temperature elevation 
naturally accelerates the change. In alkaline solutions hydr - - 

not take place to any notable extent. On the wholt 
carbohydrates may be said to ... yjyfce alkaline 

solutions, but they react readily with dilute acids. 

recognize carbohydrates they are "hydroly: - _ 
boiling- them in an acidified - I .and then the glue 
fcesl : for by meai> lepends upon 

the reduction of cupr. salts i i - - - while the aldehyde 

# on giB - gar nd star Them- 

selves do not react with Fehli: _ 

The sensitiveness of the Fehlin_ - :act that 

monosaccharides have an aldehyde grouping on the end carbon, 
which is lacking in their higher members. When an alkaline solu- 
tion of cuprie tartrate is added to an aldehyde, the aldehyde be- 
•comes oxidized to an acid, while the cupri 
cuprous state, the red color of th i . - ■ 

lesired. 

19. The Hydrolysis of Cane Sugar. Starch and Cellulose. 

Make the Fehling's test on a solution of (a> clue bbi une sugar, 

-tarch which has been "dissolved" -• I *ung a little starch into 

some cold water and then heating the mixture. 

To make the test, mix 1 c.c. of copper sulphate solution with 1 c.c. of a 
solution containing sodium potassium tartrate and *caustic soda, using 
enough of the second solution to ssolve of cuprie hy- 

droxide first formed: heat this mixture to l»oiling and add a few drops 
of the solutioi ed. If monosaccharides are present, a brick -red 

precipitate will be obtained. 

Next •\hydrolyze" some cane sugar ; dissolve a little sugar in water, 
add a few drops of dilute sulphuric acid, and boil the solution for one to 
three mir. rralize the acid with sodium hydroxide and tesl 

solution with Fehling's solution! 'Hydrolyze" some starch by acidify- 
ing the starch solution ( ! | prepared above and boiling it. It will be 
nece-- ntinue the boiling for ter. twenty minutes, because 

starch hydrolyzes more slowly than cane sugar. Test the solutio: 
Fehling's solution. 

Filter paper or cotton are examples of pure cellulose. Try to hyci' 
a sample of cellulose by keeping it in acidified water at 100 degrees: this 
may be done by placing the container ( i. e.. a test tube or a flask 
beaker or other vessel in which water is boiled. After the water in the 
- iner is hot. the container mir " | :>ered to prevent the evapora- 

tion of the water in it I -ating the cellulose for the rest of the 

laboratory period, set it aside until the next laboratory period, then boil 
again for' about two hours. Then :-- - - lution with Febling's solution. 

20. The Hydrolysis of Pcly- arid Disaccharides to Monosaccharides 

by Means of Living Organisms. 

changes of -~ r cellulose do not consist 

of one ; : : . but of several, and if the change is ar: 



Chapter XIV 235 

at different points different intermediate products ma}' be obtained. 
Thus starch, which is insoluble, may be changed to an intermediate 
soluble compound, dextrine, which is not yet a monosaccharine 
because it does not respond to the Fehling's test. Similarly, cellu- 
lose may be hydrolyzed to intermediate compounds. Of course, 
when in either case the action is continued long enough, the sub- 
stance is finally converted to a monosaccharide. 

The hydrolysis of starch and of sugar (but not of cellulose, to 
any practical extent) is also brought about by the action of 
enzymes. 

These enzymes may be produced (a) by micro-organisms, such 
as yeasts and bacteria; (b) by sprouting seeds, etc., e. g., diastase 
is formed by sprouting barley and hydrolyzes starch to a disac- 
charide: (c) by special processes of secretion in the higher ani- 
mals, e. g., ptyalin in saliva. 

For the sake of accuracy it should be mentioned that only the 
monosaccharides are directly "fermentable" into alcohol and car- 
bon dioxide. The action of yeast upon disaccharides is noticeably 
made up of two consecutive actions due to distinct enzymes which 
are both produced by the yeast plant : 

(1) The hydrolysis of the disaccharides. 

(2) The change of monosaccharide to alcohol and carbon 
dioxide. 

In sugar houses the presence of yeast germs must be carefully 
guarded against by cleanliness. ' A "sour mill," as it is called, is 
easily obtained through the fact that the alcoholic fermentation 
of sugar may be followed immediately by the acetic acid fermen- 
tation of the alcohol, because the vegetable organisms which pro- 
duce these fermentations are frequently carried about by the air. 
Acetic acid, just as other acids, catalyzes the hydrolysis of disac- 
charides to monosaccharides. The latter do not "crystallize out" 
ordinarily as the solutions are concentrated, and by making solu- 
tions more viscous they, interfere with the crystallizing out of the 
cane sugar. 

Note. — This effect of the glucose is made use of in making "pull- 
ing candy" : the sugar solution is acidified with vinegar and boiled. 
Thus, as part of the cane sugar is hydrolyzed, a syrup of non- 
crystallizing glucose is produced out of which even the cane sugar 
present does not crystallize readily. 

21. Effect of Ptyalin Upon the Solubility of Starch. 

Make a thick starch paste by mixing a teaspoonful of powdered starch 
in half a beaker of cold water and then boil for three or four minutes. 
Cool the starch paste to body temperature and divide it into two por- 
tions. To one portion add half a test-tube full of saliva. Pour each por- 
tion on dry filter papers in two separate funnels, and stand them aside 



236 Schoch: Introductory Chemistry 

for an hour, collecting the filtrates. Observe that the one to which saliva 
was added gives the larger amount of filtrate, showing that saliva has 
made the starch soluble. Test the filtrate for sugar by Fehling's test. 
The increase in solubility is due to the conversion of starch into dextrine 
and glucose. 

22. The Manufacture of Sugar. 

Sugar is obtained from cane by pressing out the juice between 
rollers, and from beets by "soaking" the sliced beets in water. In 
either case the liquid contains also some albuminous matter which 
would ferment readily; it is removed by boiling the solution to 
coagulate the albumen. A small amount of free acids present is 
neutralized with lime water, and precipitated, because the calcium 
salts formed are insoluble. The liquid, after being freed from 
the solids, is evaporated to crystallize the sugar. 

23. The Manufacture of Starch. 

The separation of starch out of corn, potatoes, rice, wheat, etc., 
requires not only the softening (soaking) and crushing of the 
grain, but also the separation of the starch from other matter — 
usually proteins. (See below.) Some of these are insoluble — for 
instance, the gluten in wheat — while others are soluble. Besides 
proteins, oils are present — particularly in the seed germs. The 
separation of these substances is essentially a mechanical one and 
consists mainly of extensive kneading of the mass and washing it 
with a stream of water: the suspended matter usually settles so 
that the starch forms a separate layer. 

To illustrate the above, make a paste of wheat flour and place it in a 
small cloth bag. Then knead this bng and contents while holding it in a 
vessel filled with water to collect starch. Finally, to remove the starch 
as thoroughly as possible from the contents of the bag, continue to knead 
it under a stream of tap water until no more starch is obtained. 

Test the starch with a drop of aqueous iodine (and KI) solution: the 
deep blue color obtained is characteristic of starch. Test the starch with 
Fehling's solution to ascertain if glucose is present. 

Test the starch water qualitatively for protein. (See below.) 

Test the contents of the bag for (a) starch; (b) protein (gluten). 

24. The Chemical Properties of Cellulose. 

As is indicated in the foregoing, cellulose is particularly re- 
sistant to the action of reagents in dilute solutions. This is well 
illustrated by the fact that cotton and linen goods in cleaning are 
boiled even in strong soap solutions. Cellulose resists the oxidiz- 
ing action of chlorine even; hence cotton and linen goods are 
bleached by means of hypochlorite solutions. 

However, cellulose is readily attacked and disintegrated by 
vapors of acids; or if, after being steeped in dilute acids, it is 



Chapter XIV 237 

allowed to dry with the acid on it. In these respects — that is, in 
its behavior with alkalies, with chlorine, and with acids, — it pre- 
sents a striking contrast to wool, which is readily attacked by 
alkalies, so that it cannot even be boiled in soap solutions; it is 
destroyed by chlorine, hence must be bleached by other means 
(hydrogren peroxide, sulphur dioxide), but it resists acids even 
when they are evaporated on its surface. 

25. The Extraction of Cellulose From Plants and Its Preparation 
for Paper Making. 

Although the woody or fibrous parts of plants are composed in 
the main of cellulose, yet they also contain other substances of 
albuminous, starchy or resinous nature, which are intimately mixed 
with the cellulose and frequently serve to bind the cellulose fibers 
together. 

Cellulose exists in plants in many different states of hydration. 
In the green, growing parts, it is largely present in a more 
hydrated form than that which corresponds to the formula 
(C 6 H 10 5 ), while wood contains a great deal in a form less hy- 
drated than that which corresponds to this formula (lignocellu- 
lose). The hydrated forms of the green parts of plants are more 
or less easily attacked by the digestive enzymes and converted to 
soluble material (digested!) while cellulose and the lignocellulose 
are practically not attacked. However, they aid mechanically in 
the digestion of other components of food. 

Pure cellulose may be prepared from plant material as follows: plant 
material is freed from the hydrated cellulose, from starch and from some 
of the protein matter by boiling it with dilute acids ( 1 per cent sulphuric 
acid or 10 drops of concentrated sulphuric acid to every 100 c.c. of water) ; 
then the residue is washed with hot water to remove the acid, and it is 
boiled in a very dilute sodium hydroxide solution (about 1 c.c. of 20 per 
cent solution to every 100 c.c. of water) : this will remove resins, oily 
matter, and the remaining protein matter. The residue is washed again 
with hot water, and finally the last traces of foreign matter — some of 
which color the material — are removed by oxidation (bleaching!) with 
chlorine: for this purpose the cellulose is steeped in a small amount o' 
dilute hydrochloric acid to which a very small amount of potassium 
chlorate has been added. This mixture is heated in a water bath for a 
few minutes, and afterwards the acid is removed thoroughly by washing 
first with water, and then with a very dilute solution of soda. The 
residue may be dried on a clock glass placed on top of a beaker half 
full of boiling water. 

In the analysis of foods and feedstuffs an amount of 1 to 5 
grams of the material is weighed, and treated as above stated, to 
remove the other materials from the cellulose. 

In the commercial preparation of cellulose from wood — i. e., for 
paper — the treatment is usually not nearly as thorough. For the 
cheapest grades of wrapping paper the fibers are simply torn apart 
by "grinding" the wood on a grindstone (mechanical pulp!). But 



238 Schoch: Introductory Chemistry 

for better grades of paper the foreign matter, which glues the 
fibers together, must be dissolved out by chemical treatment. Only 
one kind of solution is used in any case. 

In most cases this is a solution of bisulphite of calcium and of 
magnesium. These salts are cheap and very effective. A solution 
of sodium carbonate, or a solution of sodium sulphate with a little 
sodium hydroxide are used in some plants. In all cases the boil- 
ing takes place in closed vessels under pressure, — hence at as high 
a temperature as possible so that the chemical actions may go on 
as rapidly as possible. The wood is put into the boiler in the 
form of chips. 

26. Organic Compounds Which Contain Nitrogen. 

None of the organic compounds considered so far contain nitro- 
gen, yet the organic compounds which contain nitrogen are not 
only large in number, but they are very important, and a certain 
amount of them in the food of animal- and plants is absolutely 
necessary for their sustenance. The nitrogen compounds in ani- 
mal and vegetable bodies appear to be derived from ammonia by 
substitution of one or more of its three ITs by carbon groups. 
According to the basic or acidic nature of the carbon radical, the 
resulting compound will be more basic or less basic than ammonia, 
and hence its tendency to salt formation (by addition with an acid. 
e. g.. XIL. HC1) is either greater or less than that of ammonia. 
The hydrocarbon radicals of the paraffin series (CH 8 , C 2 H S , C 3 H 7J . 
etc.) are all strongly basic, and hence their nitrogen compounds 
are more basic than ammonia (e. g.. CELXIL, O.H-XH.,, 
(CH S ) 3 N). They are called "amines" and they form salts like 
this: CH,XH 2 .HC1 called methyl amine hydrochloride. When 
the "X" is connected to the carboxyl group, which is acidic in 
character, the compounds are only faintly basic, e. g.. HCO.XHo 
which is derived from formic acid HCO.OH and is called "form- 
amide." Among the important nitrogen compounds found in ani- 
mal bodies is urea. 0C(KH 2 ) 2j which is sufficiently basic to form 
a fairly stable salt. 0C(NH 2 ) 2 HC1. urea hydrochloride. In the 
vegetable bodies the alkaloids, nicotine, quinine, etc.. are the best 
known nitrogen compounds. They form stable salts with acids. 

27. Proteins. 

Most of the plant and animal tissues which contain nitrogen 
are classed together as proteins. Proteins also contain sulphur. 
The per cents of the different elements in protein compounds from 
various sources range as follows 



Carbon. 51.2 to 54.7 per cent. 
Hydrogen, 6.7 to 7.6 per cent. 



Chapter XIV 23^ 

Nitrogen, 15.2 to 18 per cent. i 
Oxygen, 20.2 to 23.5 per cent. 
Sulphur, 0.3 to 2 per cent. 

There is no marked distinction in chemical composition between 
proteins of plant and of animal origin; yet they frequently have 
different properties, and they cannot in general be substituted, 
weight for weight, one for the other in food rations, because they 
are not equally digestible, and, even after digestion, they do not 
serve equally to replace or build up animal tissues. 

Proteins, like carbohydrates, are insoluble in ether, carbon tetra- 
chloride and other special solvents for fats; hence fats may be 
readily separated from animal and vegetable tissues without dis- 
turbing the other components. 

The many different proteins which have been recognized and 
which have been given special names may be classified as follows : 

(a) Simple proteins, e. g., albumen, or egg white, gluten in 
wheat, etc. 

(b) Compound or conjugated proteins, i. e., combinations of: 
simple protein molecules with molecules of other substances, e. g.,, 
casein of milk, which is a phospho-protein. 

(c) Derived proteins, which correspond to hydrolyzed products 
of simple proteins; and they are obtainable from either (a) or 
(b), e. g., peptones, the products formed by the action of pepsin 
on proteins. 

The different proteins differ largely in solubility. Only a few- 
are soluble in water without change (e. g., albumen, a simple pro- 
teid, is soluble in water; globulin, also a simple proteid, is soluble- 
in a dilute salt solution). " These soluble proteins are changed to 
a coagulated form at higher temperatures (above 65-75 degrees 
C.) ; hence they are precipitated when their solutions are boiled. 
The chemical change produced by this boiling is a slight hydrol- 
ysis. Most proteins are soluble in either dilute acids or dilute 
alkalies, or in both, which dissolution is accompanied by a hydro- 
lytic change in the substance. 

If the hydrolytic action is continued, the proteins are finally 
broken up into soluble substances. For instance, the very insol- 
uble protein called heratine, which is the main component of nails,, 
hair, hoofs, horns, etc., may be hydrolyzed into gelatine by boiling 
water. Gelatine is insoluble in cold water, but soluble in hot 
water. By long-continued boiling, gelatine finally is hydrolyzed 
into simpler substances which are soluble in both hot and cold 
water. 



240 SCBOCS: ISTBODTTCTOET ChEMISTET 

28. The Hydrolysis of Proteins by Means of Enzymes. 

This hydrolytic char _ ;ich can be brought about 

zymes. ji - 

ibumen in hk Ae full of 

10 to lo fc 

bydrochlor in an a±r 

bath at a temperatu: - - 

lum is gradually diss . 

* 

zyme found in - 
: acid, : 

the c: 

29. The Xanthoprote : t Proteins, 

umen dissolved ■ t>b «ff 

concentrated nita Then 

add a few drops of aimnoni. yeQtm 

the addit ammom; 

prese: 

30. The Food Value of the Different Pood Constituei 

Pr 

anim: 

replace: most 

•od. 
: the digestible : 
the diges: 

and animals, the meals should be 
so d- e of all ' .e-flber 

bare certain rallies. Thus, for a man with mo: J ex- 

ratio sbonlc man wit: - ma- 

cular ratio Ld for :: 

- ' ' 7 : 

:h men have done well umic r 
' . men can exist and do fairly weL w i h 
ferably 1< .ative amounts of protein matter in 

- - " meals contain larger ratios of protein marre: 
amotmt of protein l - — 

as an eqnal amount of a carbol- 3rati — onld do. 

le from the requirement of a certain minimtim amor: 
in matter ir : main requirement that foods must 

fnl-F" in amotmt of fuel for the main- 



Chapter XIV 241 

tenance of the temperature of the body. The fuel value of food- 
stuffs may be calculated by means of Buebner's factors. These are : 

1 pound of protein or of carbohydrates gives 1860 calories; 
1 pound of any animal or vegetable fat gives 4220 calories. 

This means that these substances, when burned to water and car- 
bon dioxide, evolve this much heat. It is possible to estimate the 
fuel value of foods from these figures because the digested — assim- 
ilated — portions of food are converted almost entirely to water 
and carbon dioxide. 

The fuel value of a food may be said to be the most direct 
measure of its value. 

Ascertain the analysis of any particular foodstuff — say, of oat- 
meal — and calculate its fuel value. 

Since the quantity of food a man wishes to eat at a meal is 
generally judged by its bulk or volume, it becomes advisable to 
choose foods in different seasons or climates so that roughly equal 
volumes have greater or lesser fuel values as the weather, climate, 
or the occupation of the individual may require. 

The daily rations of men have been given by one authority 
(Atwater) to be such as to have the following fuel values: 

For a woman with light muscular exercise, 2800 calories. 
For a woman with moderate muscular exercise, 3500 calories. 
For a man with light muscular exercise, 4060 calories. 
For a man with hard muscular exercise, 5700 calories. 

31. The Composition of Food and Feed Stuffs. 

Foods and feedstuffs are ordinarily considered as made up of 
the following six "proximate" components: water, ash, fats, car- 
bohydrates, protein, and crude fiber. In Texas every bag of feed- 
stuff must be tagged with a label which states the per cents of 
these components present in the contents, as determined by the 
State Chemist, at College Station. The analysis of a foodstuff 
should report the same constituents. 

Vegetable foods furnish some protein. Wheat has a larger per 
cent of protein than any other cereal. It contains from 10 to 18 
per cent of protein (gluten) and from 65 to 70 per cent of carbo- 
hydrates exclusive of fiber. Animal foods, with the exception of 
milk, furnish practically no carbohydrates. Milk furnishes all 
essential food constituents. Since this substance is such a fre- 
qently used article of diet, a demonstration of its components is 
desirable. 

32. The Components of Milk. 

Determine the specific gravity of milk: that of fresh milk is between 
1.029 and 1.034, while that of skimmed milk is higher. 



5 : : : i . . 

-mine the amount of butter fat present, by Babo 

mused sample into a test bottle 
and add 17.5 auric ac xnd whe 

curd is dissolved, wl :n the cer _ r four minutes 

e machine used. A^d boiling fa 
filling to the neck of the bottle, and - one rnir d ■ add 

humtwmg wa~ ,f the 

- r one minute more read the Ier . 
:ese readings must be Bade at a tempera- tern 30 

and 50 de~ 
per cent of fat in the milk d 

In - - -- " 

- the chief proteid of milk. T Itdd, 

satura-: rsilk with some aewj -odium chloride 

or magnesium sulph ea—i a u g ta an : 

together. _ oth prec. 

Dissolve the preeij dilute sodium 

xide solution. Heat the soluticr - will melt and 

float ad then i cautiously w icid: 

the pr "itated a_ 

Milk also contains albumen. This will be found in the - Tate obtained 
above .pirate the albumen. This is the substance 

forms the akin wh- - boiled. 

iemonstrate the presen t j testing the same 

liquid with Fehling-'s solution. 

33. Some Chemical Proper- J.bers: Cotton. WooL Silk. 

• 
Silk - 
with I con- 

-ilphnr. It is not quite as eas 

--? jug caustic alkali 
solutions zs « 
cellulose. 

oecause tbe latter is merely cellulose in composition and 
I - 

.and 
and - ~vool on the il : if 

ignition it no particular odor, 

and leave- ~- - ^ 

. the burning of wool prodaee* 

bum; ■ iter 

r : ----:"- 
samples of the ~ 

.■_ : ;i r: -..- zzi:~ - 

- : - - - : " - - • 

■" _ f . " 

nder a m_ 



Chapter XIV 243 

Secure samples, of about one gram each, of white silk, white wool, and 
white cotton (yarn or cloth). Place these samples in small beakers, cover 
them with a ten per cent solution of sodium hydroxide, and stir the mix- 
ture so that the solution may act thoroughly on the fibers: the cotton 
will remain undissolved, but the silk and the wool will dissolve. To the 
solutions of the latter, add a little lead acetate: the wool solution will 
give a precipitate of lead sulphide, but the silk solution should give none. 

Secure a piece of cloth composed of both wool and cotton, and dissolve 
out the wool by means of a ten per cent solution of sodium hydroxide. 

Silk can be separated from wool and cotton by means of a solu- 
tion of zinc chloride which is so concentrated that it has a specific 
gravity of 1.70, and in which some zinc oxide has also been dis- 
solved. 

Wool must frequently be freed from burs and from seeds, or 
even from cotton: for this purpose, it is steeped in dilute hydro- 
chloric acid, or in dilute sulphuric acid, and then allowed to dry 
partly. On drying, the dilute acid attacks and disintegrates the 
cellulose (cotton, burs, etc.), but does not affect either wool or silk 
appreciably. 

For a demonstration, secure a bit of cotton cloth, steep it in some dilute 
hydrochloric acid, squeeze out the excess of acid and lay the cloth aside 
to dry: when dry, it will be found to easily disintegrate mechanically. 

Questions on Chapter XIV. 

1. Draw one structural possibility for oleic acid, linoleic acid 
and linoleinic acid. Draw the structural formula, large scale, of 
one molecule of olein, one molecule of palmitin, and one molecule 
of stearin. Calculate how many grams of olein will react with 
one gram of iodine. Calculate how many grams stearin will re- 
act with one gram of sodium hydroxide. In each case begin your 
calculation by stating the chemical reaction which takes place. 
Explain how stearin is made from cotton seed oil: does it need 
to be kept cold in order' to keep it in the solid form after its 
extraction ? 

2. Describe how you would extract the oil from any food ma- 
terial such as corn kernels. How is cotton seed oil refined? Ex- 
plain why the conversion of a part of the oil into soap serves to 
remove the impurities from the oil (what is the nature of the 
impurity?) and why does the refined oil keep better than the raw 
oil? Describe how to determine the pure soap material (its 
amount) in a commercial soap. Why may soap be used to meas- 
ure the amount of "hardness" in potable waters: state all you 
know concerning the nature or cause of hardness in water and 
how soap reacts with the substances in hard water. 

3. Why is the Maumene Test a logical means of examining 
oil to be used for paints? What is the action of a "japan" in 
paints? How is linoleum or oil cloth or printers' ink produced? 



9 B B • ISTK I " I O [ H33DSTKT 

:han unboiled lin- 

- - - 

31 - - a - - jii-r: 

- . _• 
iper ma sugar mann- 

■-'. -':.:■• •.'. 

- .. - 

I placed Wherein do 

- m all :eins 

- . - 

I mathem :tion 

- 

_ 

- - 

:al propel 



APPENDIX 



INTERNATIONAL ATOMIC WEIGHTS, 1918 





Symbol 


Atomic 
Weight 




Symbol 


Atomic 
Weight 




Al 

Sb 

A 

As 

Ba 

Bi 

B 

Br 

Cd 

Cs 

Ca 

C 

Ce 

CI 

Cr 

Co 

Cb 

Cu 

Dy 

Er 

Eu 

F 

Gd 

Ga 

Ge 

Gl 

Au 

He 

Ho 

H 

In 

I 

Ir 

Fe 

Kr 

La 

Pb 

Li 

Lu 

Mg 

Mn 

Hg 


27.1 

120.2 
39.88 
74.96 

137.37 

208.0 
11.0 
79.92 

112.40 

132.81 
40.07 
12.005 

140.25 
35.46 
52.0 
58.97 
93.1 
63.57 

162.5 

167.7 

152.0 
19.0 

157.3 

69.9 

72.5 

9.1 

197.2 
4.00 

163.5 
1.008 

114.8 

126.92 

193.1 
55.84 
82.92 

139.0 

207.20 
6.94 

175.0 
24.32 
54.93 

200.6 


Molybdenum 

Neodymium 

Neon 

Nickel 


Mo 

Nd 

Ne 

Ni 

Nt 

N 

Os 

O 

Pd 

P 

Pt 

K 

Pr 

Ba 

Bh 

Bb 

Bu 

Sa 

Sc 

Se 

Si 

Ag 

Na 

Sr 

S 

Ta 

Te 

Tb 

Tl 

Th 

Tm 

Sn 

Ti 

W 

U 

V 

Xe 

Yb 

Yt 

Zn 

Zr 


96.0 


Antimony 


144.3 
20.2 




58.68 




222.4 






14.01 






190 9 






16 00 






106.7 






31 04 






195 2 






39 10 


Cerium 

Chlorine 


Praseodymium 


140.9 
226.0 


Chromium 




102 9 


Cobalt 




85.45 






101 7 


Copper 




150.4 


Dysprosium 




44.1 


Erbium 




79.2 


Europium 




28.3 


Fluorine 


Silver 


107.88 


Gadolinium 




23.00 


Gallium 




87.63 


Germanium 




32.06 




Tantalum 


181 5 


Gold 


127.5 


Helium 




159 2 


Holmium 




204 


Hydrogen 




232.4 






168 5 


Iodine 

Iridium 


Tin.. 


118.7 
48.1 


Iron 




184.0 


Krypton 


Uranium 

Vanadium 

Xenon 


238.2 
51 


Lead 


130 2 


Lithium 


173 5 


Lutecium 


Yttrium 


88.7 


Magnesium 




65 37 


Manganese 




90.6 


Mercury 







246 



Appendix 



VAPOR PRESSURES 



Temperature 




Temperature 








Pressure in 
mm. of Hg 

4.60 






Pressure in 
mm of Hg 


Centigrade 


Fahrenheit 
32.0 


1 . - • Z 7 i . : 


Fahrenheit 




- 


75 _ 


22 18 


5 


41.0 


6.53 


- 


" 


23 55 


8 




8.01 


26 


78 8 


-•-. - 


10 


' ■ 


9.16 


_" 




26.50 




53.6 


10 46 


_• 


82.4 


28.10 


14 


" 


:: •: 


29 


- 


29.78 


15 


59.0 


- ' 


30 


.. . 


31 55 


16 


BQ . 




35 


95.0 


41 83 


17 


62.6 


- 


40 


104.0 


*) 


18 




15.36 


50 


122 1 


91.98 


19 


66.2 


16 35 


60 


:; 


148.79 


20 


- • > 


17.39 


70 


".'- ■ 


233.09 


21 


m - 


18.49 


80 


176 


354 64 


22 




19 66 


90 


1 A: 


52" 


23 


- 


20.89 


100 


212 


760.00 



THE METRIC SYSTEM AND EQUIVAL: 



I. Length: (a) 



(b) 



10 millimeters=l centimeter 
10 cen ti meters = 1 decimeter 
10 decimeters =1 meter 
1000 me* =1 kilometer 

1 meter =1.094 yds = 28 

39.3T in. 
1 kilometer =0.6214 m: 



::.= 



II. Voh 1000 cnbic centimeters=l li* 

1 liter=61.03 en. in.=l/'57 quart 
1 en ft=28.32 liters. 



111. ir, w ; - 



(b) 



10 milligTams=l centigram 
10 centi2Tams=--l decigram 
10 deci.2rrams =1 2Tam 
1000 srams =1 kilogram 
1 kilogram =2 b. av. 

1 lb. av. = 4o?.> ? _t 
1 oz. av. = '". ; .-rams 



Appendix 247 

relations of temperature scales 

The ordinary domestic and the engineer's scale of temperature 
is the Fahrenheit scale, upon which the freezing-point of pure 
water is 32° F. and the boiling-point under atmospheric pressure 
is 212° F. — an interval of 180°. The scientific scale is the Centi- 
grade (or Celsius) scale, upon winch the freezing-point of pure 
water is 0° C. and the boiling-point 100° C— an interval of 100°. 



180 

The degree Centigrade, therefore, is or 9/5 of 1° Fahren- 

100 

100 

heit; the degree Fahrenheit is or 5/9 of 1° C. The follow- 

180 

ing conversion formulas are useful for quickly converting temper- 
atures from one scale to the other : 

C° = 5/9 (F°— 32): F° = 9/5 (C°)+32. 



INDEX 



Acids, bases, and salts — 

definition 63 

writing formulae of 66 

solubilities 67 

acid-salts 70 

ions formed by 74 

extent of ionization 80 

table, per cent ionized 81 

Acid salts 70 

Alcohols 204 

wood alcohol 206 

ethyl alcohol 206 

qualitative test 206 

quantitative determination . . . 207 

Aldehydes 209 

Alkali metal group of periodic 

system 68 

Alkaline earth metal group ol 

periodic system 68 

Ammonia — 

reactions produced by 126 

rule for use of 128 

properties 100 

ionization relations 128 

Aromatic or cyclic compounds.. 212 

their source 213 

Atomic structure of matter 11 

Atomic weights : table of 245 

derivation of 8 to 11 

Bases : solubilities 67 

formulae and relation of oxides 

to hydroxides 70 

extent of ionization 80 

Basic hydroxides which act as 

acids 121 

Battery cells: details of — 

Daniell cell 174 

lead storage battery 176 

Battery poles or half-cells — 
how to determine their volt- 
ages < 170 

table of voltages 172 

Beaume hydrometer scale 201 

relation to specific gravity .... 202 

Bromine — 

preparation and properties. . . . 107 

hydrobromic acid 107 

Calculations based on symbols 

and equations 13 

Carbon dioxide : properties 92 

properties of solution of 94 

carbonates and bicarbonates. . . 94 



Carbon : properties, compounds, 

etc 90 

Carbon-silicon group of periodic 

system 96 

Catalyic action — 

definition and explanation .... 19 

Carbohydrates : kinds of and 
properties 233 

Cellulose : properties 236 

manufacture 237 

Chlorates : preparation, prop- 
erties 191 

Chlorine: compounds with oxygen 189 

Chlorine, preparation, properties 104 

Chromic acid and chromates — 

action as oxidizers 193 

Cloth fibers: cotton, wool, silk — 
composition and properties .... 242 

Cotton seed oil: manufacture and 

properties 221 

products of 222 

refining and bleaching 225 

Crude petroleum — 

distillation 197 

refining 199 

Crystals — 

mechanism of formation 44 

water of crystallization 46 

purifying salts by recrystalli- 
zation 50 

Disinfection with formaldehyde. 210 

Electric current: explanation of 

passage through solutions .... 78 

Electricity: nature of 160 

Electrolysis of hydrochloric acid: 

quantitative 165 

Electrolysis of various substances 
and explanation of accom- 
panying changes ....161 to 165 
Elements — 

their recognition and distinc- 
tion from compounds 7 

number and kinds of 7 

Equilibrium and its significance. 28 

first example 29 

second example 47 

third example 59 

law of mass action applied to. 58 
Ether: ethyl or sulphuric-prepa- 
ration 208 

Feedstuff law, Texas 241 



250 



Index 



Flash point of oils 200 

Fluorine: properties 108 

hydrofluoric acid 108 

Food — 

value of different constitu 

of 240 

rations for men 241 

composition of various food 

and feedstuff's 241 

Forms of matter: solid, liquid. 

and gaseous 1 

Formulae of compounds: figured 
out from valences of constit- 
uents 65 

molecular-kinetic struc- 
ture 39 

of l>ehavior 41 

reduction of volumes t<> -tand- 

ard conditions 41 

volume: relations shown by 

equations 116 

o! frram molecule 110 

ine: legal definition in 
Texa a 

Halo- ./roup of periodic 

item 103 

properties 100 to 10<* 

Heat in chemical changes 23 

Hydration of oxide-: forming 

acids and bases 00 

Hydrochloric acid: preparation 

and properties 106 

Hydrogen — 

preparation 34 

properties 37 

quantity evolved by a metal . . 36 
Hydrogen sulphide — 

reactions produced by 130 

effect of acid upon it = action 

in solution 131 

action of oxidizers upon 137 

Hydroxides: relation to oxides 70 

Hypochlorites 190 

Iodine: preparation, properties. 107 

hydrochloric acid 107 

Ionization: fundamental facts 

and notions 74 

determination of fractions of 

electrolyte> ionized 75 

table of ionization values 81 

Ions: manner in which they form 

compound- 82 

fundamental relation between 
ions which brings about 
metathetical reactions 83 



Law of definite proportion 5 

Law of indestructibility of mat- 
ter * 4 

Law of mass action 58 

Lin-eed oil: preparation and 

properties 22^ 

analysis of 230 to 233 

Liquids : molecular structure and 
details of condensation from 

42 

Lubricating oil: viscosity test. 200 

M action law: explanation... 58 

illustration of 84 

Metals: order of reactivity to 

form simple compounds 32 

reaction with acids: general 

facts 34 

reaction with water or steam 51 
Metathetical reactions — 

definition 07 

condition which brings about 
- 1>et\veen acids. 

1 salts 83 

Milk: composition of 241 

legal requirements in Texas . 241 
ilar weights — 

hi-tory of determination 112 

procedure for determination. . . 115 

Nitric acid — 

action a- oxidizing agent 183 

table of reduction products. . . 183 

reactions of 184 to 186 

Nitrogen : properties 102 

in group of periodic system. . . 102 

Normal -olutions — 

definition. explanation. and 

preparation 124 

Xote book: direetions for 2 

Oils and fats of animal and vege- 
table origin 220 

Oil in cotton seed — 

determination of its quantity. . 224 

Organic acids: their general com- 
position 210 

Organic compounds: main classes 195 

Oxidation : definition 178 

Oxidation-reduction reactions : 

tlu>ir relation to battery cells 179 

Oxidizing and reducing agents — 
table of their reactions and 

forces 172 

their complete ionization or 
formation of elemental ions. 181 

OxyL^n : its preparation by heat- 
ing some of its compounds. . 20 



Index 



251 



Oxygen — Continued 

properties 21 to 22 

in group of periodic system. . . 99 

Oxy -halogen compounds : table . . 1 89 

Paper : manufacture 237 

Paraffin series of organic com- 
pounds — 

structure and general formula. 196 

properties 197 

Periodic system of the elements. 13 

Harkins' model of 14 

Table of 16 

notes on alkali metal group ... 68 

notes on alkali earth group ... 68 

notes on carbon group 96 

notes on halogen group 103 

notes on nitrogen group 102 

notes on oxygen group 99 

Permanganates as oxidizers 192 

Poles of electric cells — 

definition of "signs" of poles 
in battery and electrolytic 

cells 159 

Proteins 238 

Qualitative analysis — 

the five groups of metals 138 

directions for dissolving sam- 
ples 139 

group 1: precipitation of 141 

group 1 : identification of mem- 
bers 142 

group 2: precipitation 142 

group 2: identification of mem- 
bers 143 

group 3; precipitation 145 

group 3: identification of mem- 
bers 146 

group 4: precipitation 149 

group 4: identification of mem- 
bers 151 

group 5 : identification of mem- 
bers 152 

anions: identification 153 

Reduction of metal oxides 52 

Salts- 
solubility change with temper- 
ature of some common salts. 49 
solubilities at ordinary temper- 
ature 67 

acid salts 70 

extent of ionization 80 

table, per cent ionized 81 



Separation of metal ions in solu- 
tions — with ammonia 130 

with hydrogen sulphide 135 

with sodium hydroxide 121 

Soap : manufacture 225 

kinds of 226 

preparation of 227 

analysis of 227 

Sodium hydroxide — 

reactions produced by 118 

table of products formed 119 

its commercial preparation... 123 

Solids: amorphous and crystal- 
line 44 

Solubilities of acids, bases, and 

salts 67 

Solutions — 

molecular structure 45 

boiling points, freezing points, 

and osmotic pressures 45 

determination of solubility .... 47 
solubility change with temper- 
ature 48 

Starch : properties 234 

manufacture 236 

Silica and silicates 109 

Sugar-chemical properties 234 

manufacture 236 

Sulphur: properties and com- 
pounds of 96 

as a member of periodic system 99 

Sulphur dioxide : properties 97 

Sulphides — 

colors of various metal sul- 
phides 133 

reactivity with main solvents. 133 

Sulphuric acid: action as oxidiz- 
ing agent 187 

preparation and properties. . . 98 

Symbols and equations 12 

Temperature scales: relations of. 247 

Tar oil : uses of 215 

Transport of ions: by electrolysis 

or battery action 161 

Unsaturated organic compounds. 202 

Valence: definition and illustra- 
tion 33 and 64 

Water: ratio, by weight, of 

oxygen to hydrogen in 55 

Water vapor, pressure of: table. . 246 

Weights and measures: metric 

system and equivalents 246 

Wood distillation: products of.. "217 



